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Notes: The reaction was investigated in the gas phase over the range 80-225°C using the photolysis of heptafluoroisopropyl iodide as the source of radicals. The rate constant, based on the value of 1013.36 cm3 mol-1 s-1 for the recombination of i-C3F7 radicals, is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(}{{k_3 } \mathord{\left/ {\vphantom {{k_3 } {{\rm cm}^{\rm 3} }}} \right. \kern-\nulldelimiterspace} {{\rm cm}^{\rm 3} }}{\rm mol}^{ - 1} {\rm s}^{ - 1}) = (13.10 \pm 0.20) - {{(14000 \pm 280)} \mathord{\left/ {\vphantom {{(14000 \pm 280)} \theta }} \right. \kern-\nulldelimiterspace} \theta } $$\end{document} where θ = 2.303 RT/cal mol-1. Arrhenius parameters for chlorine abstraction from CCl4 by CF3, C2F5, n-C3F7, and some hydrogenated radicals are compared.

Notes: We present a kinetic study of the reactions of ground-state sodium atoms with the molecules CH3F, CH3Cl, CH3Br, HCl, and HBr at elevated temperatures (537-966 K). Na(32S1/2) was generated by the pulsed irradiation of various sodium halide vapors and monitored by time-resolved atomic resonance absorption of the unresolved D-lines at λ = 589 nm [Na(32PJ) ← Na(32S1/2)] in the “single-shot mode.” The photoelectric signals were amplified without distortion, captured, and digitized in a transient recorder interfaced to a microcomputer for data analysis. Absolute second-order rate constants were measured at various temperatures in each case, yielding the following Arrhenius parameters (kRX = A exp(-E/RT), errors 1σ): which constitute, to the best of our knowledge, the first direct measurements of these quantities. The reaction between Na and HBr demonstrated anomalous behaviour which is discussed in terms of potential surfaces that have been calculated previously for this type of collisional process. The data are compared with analogous results for Na + CF4, CF3Cl, and CF3Br and with single-temperature measurements on diffusion flames.

Notes: It was found that the pyrolysis of [5-14C]-1-pentene gives radioactive 1,3-butadiene. This result can be explained in terms of a sequence of free radical rearrangements of 1-penten-3-yl radicals. From this and additional information on isotope distribution in butadiene formed from different deuterated 1-pentenes, we conclude that homoallylic rearrangement of 1-penten-4-yl and 2-penten-5-yl radicals is the dominant route for their consumption.

Notes: The gas phase elimination of methyl 4-chlorobutyrate and methyl 5-chlorovalerate has been reexamined, in a static system and seasoned vessel, over the temperature range of 419.6-472.1°C and pressure range of 45-108 torr. The reactions, under maximum inhibition with propene, are homogeneous, unimolecular, and obey a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for methyl 4-chlorobutyrate, log (k1(s-1) = (13.41 ± 0.60) - (226.8 ± 8.2) kJ/mol/2.303RT; and for methyl 5-chlorovalerate, log k1(s-1) = (13.20 ± 0.02) - (227.6 ± 0.3) kJ / mol / 2.303RT. The pyrolysis rates are found to be about a half of the rates reported in a previous work. As already advanced, the carbomethoxy substituent appears to provide anchimeric assistance in the elimination process, where normal dehydrochlorination and lactone formation arise from an intimate ion pair type mechanism. The partial rates towards each of these products have been determined and reported.

Notes: Experiments with propane-ethylene mixtures in the temperature range 760-830 K resulted in refinement of the role of ethylene inhibition in the decomposition of propane. The source of the rate-reducing effect of ethylene is the reaction This replaces the decomposition chains more slowly by means of the reactions than H-atoms do by direct H-abstraction from propane. Analysis of the ratios of the product formation rates showed that the selectivity of the ethyl radical for the abstraction of hydrogen of different bond strengths from propane was practically the same as that of the H-atom. The ratio of the rate constants of hydrogen addition to ethylene and methyl-hydrogen abstraction from propane by the H-atom (3) was determined \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{k_3 }}{{k_8 }} = 10^{5.89 \pm 0.05} \exp ( - 30.8 \pm 1.1{\rm kJ mol}^{{\rm - 1}} /RT) $$\end{document} as was that of the decomposition and the similar H-abstraction of the ethyl radical \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{k_3 }}{{k_8 }} = 10^{5.11 \pm 0.61} \exp ( - 129 \pm 10{\rm kJ mol}^{{\rm - 1}} /RT){\rm mol}^{{\rm - 1}} {\rm dm}^{\rm 3}. $$\end{document}Interpretation of the influence of ethylene required the completion of the mechanism with further initiation of the reaction besides termination via ethyl radicals.

Notes: Reaction data described by the second-order growth function A(t) = A∞(αt) (1 + αt)-1, where A∞ is the ultimate value of the product concentration A(t), can be linearized by plotting a suitable function F(t) against the time (t). The slope of the straight line obtained is (2α), where α is the product of the rate constant (k2) and the initial concentration of either reactant, with the result that k2 can be determined without knowledge of Aϰ. Optimal determination of the parameter α requires that data taking be limited to the interval 0 ≤ t ≤ T, where (αT) is approximately 4.0. Numerical data derived from an experiment on the exchange of lead by zinc ions in the enzyme carbonic anhydrase are analyzed to illustrate the method. The effects of small errors in the initial concentrations and of small deviations from second-order kinetics are briefly discussed.

Notes: On the basis of the thermal decomposition of mixtures of propylene and propane with molar ratios of 0.0-0.33 in the temperature range 779-812K, the influencing functions describing the inhibition by propylene of the decomposition of propane were determined. The rate-reducing effect is explained mainly by the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + {}^.{\rm R} \longrightarrow {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 5} + RH $$\end{document} (in which .R = .H, .CH3 and 2-Ċ3H7) and also by the addition reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + {}^.{\rm H} \to 1 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \to 2 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7}. $$\end{document} It was established that the bulk of the allyl radicals formed \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 8} + {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 5} \to 1 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \to 2 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} $$\end{document} participate in the chain step, but, due to their lower reactivity, they restore the decomposition chain more slowly than the original radicals do.From the characteristic change in the ratio υCH4/υH2, the rate ratios of hydrogenabstraction reaction by radicals from propylene and propane could be determined. In these reactions there was no significant difference between the selectivities of the radicals. For an interpretation of the changes, the decomposition mechanism must be completed with the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + 2 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} \to 1 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 6}. $$\end{document}Evaluation of the influencing curves revealed that the initiation reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 6} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} \to {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 5} + {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 7} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 8} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} \to {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 7} + {}^.{\rm C}_{\rm 3} {\rm H}_{\rm 7} $$\end{document} must be taken into account.By parameter estimation we have determined the rate ratios characterizing the above initiation reactions, the unimolecular decomposition of propane, hydrogen abstraction by radicals from propane and propylene, intermolecular isomerization of the 2-propyl radical via propane and propylene, and abstraction of propane hydrogens by the ethyl and methyl radicals; these are given in Tables II.

Notes: The pyrolyses of four alkyl allyl sulfides with substituents on the α—C atom of the alkyl moiety have been studied in a stirred-flow system over the temperature range 340-400°C and pressures between 2 and 12 torr. The only products formed are propene and thioaldehydes. The reactions showed first-order kinetics with the rate coefficients following the Arrhenius equations: Chloromethyl allyl sulfide: \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm s}^{{\rm - 1}}) = 10^{10.74 \pm 0.23} \exp ( - 144 \pm 3){\rm kJ/mol}RT $$\end{document} Cyanomethyl allyl sulfide: \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm s}^{{\rm - 1}}) = 10^{10.20 \pm 0.19} \exp ( - 129 \pm 2){\rm kJ/mol}RT $$\end{document} 1-cyanoethyl allyl sulfide: \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm s}^{{\rm - 1}}) = 10^{11.09 \pm 0.18} \exp ( - 141.5 \pm 2.2){\rm kJ/mol}RT $$\end{document} Neopentyl allyl sulfide: \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm s}^{{\rm - 1}}) = 10^{10.54 \pm 0.24} \exp ( - 144 \pm 3){\rm kJ/mol}RT $$\end{document}The effects of these and other substituents on the reactivity is discussed in relation with the stabilization of a polar six-centered transition state. The results support a non-concerted mechanism where the 1-5 α—H atom shift is assisted by its acidic character.

Notes: The first stage thermal reactions of CF2CICH3 in the presence of chlorine have been studied between 554 and 614 K. These are and \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CF}_{\rm 2} {\rm CICH}_{\rm 3} {\rm + CI}_{\rm 2} \to {\rm CF}_{\rm 2} {\rm CICH}_{\rm 2} {\rm CI + HCI} $$\end{document} Rate equations derived from a radical mechanism are shown to fit the experimental results. Values of Arrhenius parameters for the decomposition of the CF2ClCH2. radical and its reactions with Cl2 and Cl are given.

Notes: Following the kinetic investigation of the solvolysis of a range of cobalt(III) complexes in mixtures of water + cosolvent wherethe cosolvent enhances the solvent structure and decreases the dielectric constant, kinetic data are now reported for such a solvolysis in water + urea where urea acts as a structure breaker and enhances the dielectric constant. A plot of log (rate constant) against reciprocal of the dielectric constant shows that differential effects of changes in solvent structure occur between the initial and the transition states and, as in theinvestigations using structure-enhancing cosolvents, the principal effect of change in solvent structure on the cobalt(III) cation occurs on the penta-coordinated ion in the transition state.

Notes: Rate constants have been measured for the reactions of four hydrocarbon radicals with O2 in the gas phase at room temperature. Laserflash photolysis was used to generate low concentrations of radicals. A photoinization mass spectrometer followed the radical loss as a function of time. The measured pseudo first-order decay rate of the radical and the absolute oxygen concentration were combined to give the absolute rate constants (in units of 10-12 cm3 molec-1 s-1): isobutyl (2.9 ± 0.7); neopentyl (1.6 ± 0.3); cyclopentyl (17 ± 3); and cyclohexyl (14 ± 2). The cycloalkyl radicals have rate constants similar to those of other secondary radicals. However, the isobutyl and neopentyl radicals react more slowly than similar primary radicals. These new rate constants are compared in Figure 2 with the recently published correlation of reactive cross section with radical ionization potential.

Notes: The photooxidation of allyl chloride was studied by irradiation either in 100-L Teflon bags or in a 22.7-m3 Teflon smog chamber in the presence of added NOx. In the absence of added hydrocarbons, the reaction involves a Cl atom chain, which leads to a highly reactive system. A reaction mechanism is presented to account for the following photooxidation products: chloroacetaldehyde, formaldehyde, 1,3-dichloroacetone, 3-chloroacrolein, acrolein, glyoxal, chloroperoxyacetyl nitrate, and peroxypropenyl nitrate. The rate constant for OH reaction with allyl chloride at 298 K was measured by a relative rate method under conditions where the Cl atom chain length was small and was found to be kOH = 1.7 × 10-11 cm3 molecule-1 s-1. The rate constant for O3 reaction with allylchloride at 298 K was found to be kO3 = 1.5 × 10-18 cm3 molecule-1 s-1.

Notes: The oxidation of primary alcohols by sodium N-chloroethylcarbamate in acid solution, results in the formation of corresponding aldehydes. The reaction is first order with respect to the oxidant and alcohol. The rate increases with an increase in acidity. The oxidation of α,α-dideuterioethanol exhibited a primary kinetic isotope, kH/kD = 2.11 at 298 K. The value of solvent isotope effect k(H2O)/k(D2O) = 2.23 at 298 K. Addition of ethyl carbamate does not affect the rate. (EtOC(OH)NHCl)+ has been postulated as the reactive species. Plots of (log k2 + Ho) against (Ho + log[H+]) are linear with the slope, φ, having values from 1.78-1.87. This suggested a proton abstraction by water in the rate-determining step. The rates of oxidation of alcohols bearing both electron-withdrawing and electron-donating groups are more than that of methanol. A concerted mechanism involving transfer of a hydride ion from the C—H bond of the alcohol tothe oxidant and removal of a proton from the O—H group by a water molecule has been proposed.

Notes: A theoretical treatment is given for fast, multiple bond-switching reactions, such as NO + NH2 → N2 + H2O. These reactions are characterized by all or most of the bonds being broken. The collision complex involved (whether long or short lived) is shown to be extremely anharmonic. Consideration of the master equation describing the competing processes of complex formation, internal rearrangement and collisional deactivation yields easily applied sufficient conditions for the recombination rate coefficient being independent of pressure.

Notes: Equilibria and rates of interconversion between monomeric and dimeric glyoxal were measured in aqueous solution. The equilibrium constant [G2]/[G1]2 was 0.56 M-1 at 25°C, and was hardly affected by changes of ionic strength and pH but increased rapidly with increase of temperature. The rate of depolymerization was first-order in dimer, with the pseudo first-order rate coefficient in the pH range 1.3-7.8being of the form b1[H3O+] + b2 + b3[OH-]/(1 + b4[OH-]) + b5[OH-]. Coefficients b1 and b2 were more strongly affected by changes of temperature, though [OH-] was much the more effective catalyst. This rate form has not previously been observed for monomer-dimer inter-conversion of α-hydroxycarbonyls and α-dicarbonyls or for related reactions such as mutarotations and hydrations. Equivalent rate forms arisefrom reactions where an intermediate at steady state and low concentration is produced.

Notes: Conditions leading to an explosive reaction of carbon monoxide and oxygen in the presence of small amounts of water have been examined at temperatures of 973 and 1048 K. Carbon monoxide and water were formed in the presence of oxygen by reaction with a thin film of carbon deposited on a quartz vessel. The carbon provided a reactive and reproducible surface, giving aconsistent rate of termination and thus allowing a quantitative descriptionof the conditions at the explosion in the region of the first limit. Calculations of the rates of the various branching and termination reactions at the onset of the explosion showed that the simple mechanism described earlier was still adequate to explain the reaction at temperatures up to 1050 K. From experiments with inert gases the transition from the first explosion limit to the region of the second explosion limit was demonstrated.

Notes: The kinetics of the gas phase reaction of OH radicals with dimethyl sulfide (CH3SCH3) have been studied at various temperatures and total pressures using two relative rate methods and a flash photolysis technique. For the relative rate methods, rate constants were measured at 296 ± 2 K as a function of the O2 pressure at a total pressure of ca. 740 torr. Data from these three experimental techniques were not in agreement. It is concluded that the relative rate techniques are subject to secondary reactions, possibly involving CH3S radicals. A rate constant of (2.5-0.6+0.9) × 10-12 e(130 = 102)/T cm3 molecule-1 s-1 obtained using the flash photolysis-resonance fluorescence data in the absence of O2, and which is in agreement with the lower range of values previously reported in the literature, is recommended.

Notes: A discussion of reactants vibrational energy and temperature dependence of reactive rate constants for the hydrogen atom hydrogen molecule reaction is presented for a matrix of values calculated at 0 〈 v 〈10 and temperatures in the range from 300 K to 4000 K. A parametrization ofthe results is attempted. A comparison with rate constant values obtained from an approximate quantum treatment is also reported.

Notes: The Rotating-Rod Model is modified to make the adjustable α parameter which appears in the treatment energy dependent. Its predictions for opacity and excitation functions compare well with quasi-classical H3 trajectory results, for translational and vibrationalenergy variations and isotopic mass effects. The Frozen-Orientation Model in its present form is incapable of such an agreement for mass combinations other than H + D2. It is suggested that the decreaseof α with energy can be interpreted as a transition from adiabatic tosudden behavior, where alignment is only on the average, and much energy isdeposited in the bending modes. This is supported by a correlation between α and the average final rotation.

Notes: Recent dynamical computations on the LSTH and PK(II) potential energy surfaces are analyzed in terms of different properties of the surfaces. Differences in the bend level structure of resonances are found tobe due to the weaker vibrational force constant at the saddle point of the LSTH surface. The importance of including van der Waals wells in the potential energy surface is demonstrated by analysis of quantal resonances in thecollinear Mu + D2 reaction.

Notes: The Kinetics of the binding of librium to bovine serum albumin were investigated at an ionic strength of 0.15 M, in the pH-range between 5.5 and 10.5, using the temperature-jump method. Two relaxation times were observed. The first, rapid one is assigned to the equilibrium between reactants and complex, whereas the second, slower relaxation time measures a conformational change of this complex. Both relaxation times are independent of pH up to about 8.0 when they increase sharply to a new plateau at a pH of about 9.3. A possible parallelism between this behavior and the N ⇌ B transition of albumin is discussed. The overall equilibrium constant K, as well as the equilibrium constant between the two conformers, K2, were estimated from our kinetic results. Whereas the change of K with changing pH was within the experimental error, the equilibrium between the two conformers of the complex is somewhat shifted by an increase of the pH. At all values of pH, however, they are present in comparable concentrations. The value of K was also measured spectrophotometrically. The results of the two methods showed reasonable agreement. The relaxation times were affected very little by a change in temperature between 12 and 25°C from which it is concluded that the isomerization has a high negative value of ΔS

Notes: Trichloromethylperoxyl radicals were produced by pulse radiolysis of air saturated solutions containing CCl4. The rate constants for the reaction of CCl3O2 radicals with zinc tetraphenylporphyrin (ZnTPP) were determined in various solvents. They were found to vary between 3 × 107 and 3 × 109 M-1 s-1. The changes in rate constants result from complexation of ZnTPP with the different solvents, but did not correspond to changes in redox potential of ZnTPP. The rate constants were found to depend on the strength of the axial complexation, indicating an inner sphere mechanism whereby the radical binds to the metal prior to electron transfer.

Notes: The kinetics and mechanism of electron transfer between stable verdazyl radicals via bridge Mn(II), Co(II), Ni(II), Cu(I), and Zn ions have been studied in the range 280-330 K using the stopped-flow technique. It was found that the kinetic features of the reactions could be described in terms of the Marcus theory. The reorganization energy of the inner coordination sphere (ICS) of intermediate complexes was estimated from the reported data on the energy of release of various ligands from the ICS of similar complexes. The rest of the kinetic parameters (solvent reorganization energy, transmission coefficients, enthalpy, and entropy of activation) were determined from Marcus equations and from plots of rate constant versus temperature, “standard” free energy, and polarity of the medium. It was also found that the reactions under consideration are nonadiabatic and the transmission coefficient value depends on the mean lifetimes of ligands in the ICS.

Notes: The kinetics of the oxidation of aliphatic aldehydes, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, and trichloroacetaldehyde by Peroxomonosulphate (PMS) was carried out in aqueous perchloric acid medium (0.1-1 M H+) at constant ionic strength of 1.2 M in the temperature range 10°-60°C. The reactions of all the aldehydes were found to obey a total second-order kinetics, first order each with respect to [Peroxomonosulphate] and [aldehyde]. Acetaldehyde, propionaldehyde, and n-butyraldehyde exhibited acid catalysis with the concurrent occurrence of acid-independent reaction path conforming to the rate law \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm PMS]}}}{{dt}} = k_a [{\rm PMS] [aldehyde] [H}^ +] + k_b [{\rm PMS] [aldehyde]} $$\end{document} Formaldehyde was found to undergo oxidation only by acid-dependent path (kb = 0) and trichloroacetaldehyde exhibited only the acid-independent reaction path (ka = 0). The products of oxidation were found to be the respective carboxylic acids in each case. The stoichiometry of the reaction, [Peroxomonosulphate]:[Aldehyde] = 1:1, indicated the absence of carbonyl-assisted decomposition and self-decomposition of peroxomonosulphate. The kinetic and thermodynamic parameters evaluated pointed to the mechanism of a fast nucleophilic attack of the oxidant on the aldehyde followed by slow acid catalyzed and/or uncatalyzed decomposition of the intermediate to product. A sharp comparison is made with the corresponding reactions of the similar peroxides, S2O82- and H2PO5-.

Notes: Procedures are discussed to correct for nonideality in a shock tube used in the reflected mode in conjunction with flash photolysis and atomic resonance absorption to measure chemical kinetics of atoms at high temperatures. Experimentally, pressure time profiles for the incident and reflectedshock regions are made close to the location of the observation windows through which absorbance is measured. The corresponding temperatures are calculated from the adiabatic equation of state. Justification for this procedure is provided by extending Mirels' boundary layer theory to take intoaccount interaction of the reflected wave with the flowing gas in the free stream and in the boundary layer. These theoretical methods are described for calculating the thermodynamic and hydrodynamic states behind the reflected wave from initial values of pressure and temperature and the measured velocity of the incident wave. The implication of these results to kinetic measurements at high temperature is discussed.

Notes: The reactants, products, and saddle point for the reaction H2 + CN → H + HCN have been studied by ab initio calculations. The computed structures, frequencies, and energetics are compared directly to available measurements and, indirectly, to experimental rateconstants. The theoretical rate constants used in the comparison are calculated with conventional transition state theory. By reduction of the computed reaction barrier to 4.1 kcal mol,-1 good agreement with experimental rate constants is obtained over a 3250-K temperature range. This computed rate constant is well represented by the form 4.9 × 10-18 T2.45 e-1, 126/T over the temperature range of 250 K-3500 K. Substantial reaction rate curvature is found due to low-frequency bending modes at the saddle point. The results for this reaction are compared to other abstraction reactions involving H atom transfer to identify correlations between reaction exothermicity and both abstraction barriers and reaction rate curvature.

Notes: The rate constants of O2(1Δg) with aliphatic alcohols, terpenes, unsaturated hydrocarbons, chlorinated hydrocarbons, oxygen, and diamines have been studied in thepresence of NO2. The rate constants for oxygen, 1,2-ethane diamine, and 1,2-propane diamine are (9.9 ± 0.4) × 102, (8.7 ± 0.7) × 104, and (1.4 ± 0.3) × 104 1/mol/s, respectively. The rate constants for all other compounds are less than the oxygen rate constant.

Notes: Rate constants for overall H-atom abstraction by hydroxyl radicals from C—H and O—H bonds are estimated for alkanes, haloalkanes, aldehydes, ketones, ethers, alcohols, nitriles, and nitrates over thetemperature range 250-1000 K. These estimated rate constants utilize the modified Arrhenius expression K = A'T2e-E'/T in combination with the recommendations given in the recent review and evaluation of OH radical kinetics of Atkinson [1]. This estimation procedure gives good agreement, generally to within better than a factor of 2, of the estimated rate constants with theserecommendations.

Notes: The thermal decomposition of propanoic acid dilute in argon has beenstudied in a single-pulse shock tube over the temperature range of 1100-1500 K and over the pressure range of 14-18 atm. The decomposition kinetics have been satisfactorily computer modelled by means of afree radical mechanism involving H and OH chains.Recent single-pulse shock tube product analyses of acetic acid decomposition have been computer modelled using a free radical mechanism for decarboxylation coupled to a unimolecular dehydration reaction.A comparison between the thermal decomposition kinetics of the C1—C3 alkanoic acids is made. The present studies do notprovide evidence for the participation of transition states involving a pentavalent carbon atom in the pyrolyses of the lower alkanoic acids.

Notes: The bimolecular reactions in the title were measured behind shock waves by monitoring the O-atom production in COS—O2—Ar and CS2—O2—Ar mixtures over the temperature range between 1400 and 2200 K. A value of the rate constant for S + O2 → SO + O was evaluated to be (3.8 ± 0.7) × 1012 cm3 mol-1 s-1 between 1900 and 2200 K. This was connected with the data at lower temperatures to give an expression k2 = 1010.85 T0.52 cm3 mol-1 s-1 between 250 and 2200 K. An expression of the rate constant for CS2 + O2 → CS + SO2 was obtained to be k21 = 1012.0 exp(-32 kcal mol-1/RT) cm3 mol-1 s-1 with an error factor of 2 between 1500 and 2100 K.

Notes: The kinetics of the gas phase reaction between NO2 and CF2CCl2 has been investigated in the temperature range from 50 to 80°C. The reaction is homogeneous. Three products are formed: O2NCF2CCl2NO2 and equimolecular amounts of CINO and of O2NCF2C(O)Cl. The rate of consumption of the reactants is independent of the total pressure, the reaction products, and added inert gases and can be represented by a second-order reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm NO}_{\rm 2}]}}{{dt}} = - 2\frac{{d[{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}]}}{{dt}} = k[{\rm NO}_{\rm 2}][{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}] $$\end{document}However, the distribution of the products is influenced by the pressure of the present gases, which favor the formation of the dinitro-compound in a specific way. The effect of CF2CCl2 is the greatest. In the absence of added gases, the ratio of O2NCF2CCl2NO2 to that of O2NCF2C(O)Cl is proportional to (CF2CCl2 + γP products).The experimental results can be explaned by the following mechanism: P and X represent the products and the added gases: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm NO}_{\rm 2}]}}{{dt}} = - 2\frac{{d[{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}]}}{{dt}} = k_1 [{\rm NO}_{\rm 2}][{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = 3.16 \pm 0.5 \times 10^6 \exp ( - 10500 \pm 1000{\rm cal/}RT){\rm M}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \gamma }_{{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2} } :{\rm \gamma }_P :{\rm \gamma }_{{\rm C}_{\rm 2} {\rm F}_{\rm 5} {\rm CI}} :{\rm \gamma }_{{\rm CCL}_{\rm 3} } :{\rm \gamma }_{{\rm CF}_{\rm 4} } :{\rm \gamma }_{{\rm N}_{\rm 2} } = 1:0.22:0.15:0.14:0.054:0.015 $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \gamma }_{{\rm NO}_{\rm 2} } 〈 0.01 $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 = 1.4 \pm 0.3 \times 10^8 {\rm s}^{{\rm - 1}} $$\end{document}

Notes: Nascent product quantum state distributions have been measured for reactive, H + D2 → HD + D, and inelastic, H + D2 → D2

Notes: The collision induced dissociation of H2 by H atoms was studied by quasiclassical trajectories using the Liu-Siegbahn-Truhlar-Horowitz potential energy surface. Dissociation cross sections were obtained for five highly internally excited initial states of H2 for translational energies up to 100 kcal mol-1. Rate constants for dissociation out of these states were calculated for temperatures of 1000 to 10,000 K. Initial internal energy strongly enhances the probability of collisional dissociation, vibrational energy being more effective than rotational. The results are compared to those from a similar study of the H2-He system, and are discussed in relation tothe respective potential energy surfaces. The implications for the kineticsof thermal dissociation are also considered.

Notes: For the rate constant of addition of tert-butyl radicals to acrylonitrile at T = 300 K in solution modulated ESR spectroscopy and muon spin rotation yield 106 M-1 s-1 and 2.4 × 106 M-1 s-1. The addition of pivaloyl radical to acrylonitrile proceeds with Arrhenius parameters log A/M-1 s-1 = 7.7 and Ea = 11.5 kJ/ mol. The results are discussed in terms of polar effects in radical addition reactions.

Notes: In this paper, rate parameters are extracted from fluorescene decay data in the framework of Feedback-Type Kinetics (k8 〈 k4). The exciplex dissociation (k4) and fluorescene decay rate constants (k8) have been obtained for the five following systems: For this task we have added to the straight line method of Ware which is valid in certain cases only at high perturber concentrations, a new but similar Taylor series method applicable at low concentrations. Thereafter, a safer and more general method of kinetic analysis based on a quasi-linear χ2 minimization procedure has been developed and applies to data in any range of concentration.

Notes: In this article we briefly discuss a number of promising approaches to the formulation of a general, numerically exact, quantum mechanical theory of fully three-dimensional reactive atom-diatom collisions. It is noted that the ability to treat the three-dimensional H + H2 exchange reactions is pre-requisite to any demonstration of the success of a general quantum mechanical formalism for reactivescattering. However, it is also noted that the time has come for any such theory to further demonstrate the ability to go beyond this basic, elementary atom-diatom exchange reaction. It is speculated that there now exist a number of approaches which can potentially provide such a general framework for quantum reactive scattering theory. Finally, a new generalizationof the Faddeev formalism for such systems, which is capable of inclusion ofthree body forces with a completely general form for the potential surface, is presented.

Notes: The kinetics of hydrolytic cleavage of saccharin has been studied at 60°C within the [ŌH] range of 0.1 to 3.0 M. The observed pseudo first-order rate constants, kobs, follow an empirical relationship: kobs = B[ŌH] + [C[ŌH]]2. The B and C terms are attributed to the formation of dianionic and trianionic tetrahedral intermediates on the reaction path. It is concluded that the ionized form of saccharin is the major reacting species under the present experimental conditions. The positive ionic strength effect and the negative effect of 1,4-dioxan on the rate of hydrolysis favor the proposed reaction mechanism. The analysis of the observed activation parameters indicates that the increase in the contribution of C term to kobs causes the slight increase in both ΔH* and ΔS*. A significantly large negative value of ΔS* favors the proposed mechanism.

Notes: Rate constants for one-electron oxidation by the methylperoxyl radicals (CH3O2, HOCH2O2, -O2CCH2O2, and CCI3O2) in aqueous solutions have been measured by pulse radiolysis and found to be in the range of 3 × 105 to 6 × 108 M-1 s-1 for compounds with redox potentials between 0.6 and 0.1 V. Substitution on the methylperoxyl radical with OH or CO2- has only a minor effect on the rate of oxidation but substitution with three chlorines increases the rate constants by two orders of magnitude. The redox potential of the CH3O2 radical is estimated to be 0.6-0.7 V.

Notes: The decomposition reactions of N-bromodiethanolamine, N-bromoethylethanolamine, and N-bromomethylethanolamine in aqueous solution have been studied kinetically under various experimental conditions. The results support a proposed reaction mechanism in which the rate controlling step is assumed to be the formation of an imine which is then hydrolyzed to the final decomposition products.

Notes: We have studied the oxidation of benzyl alcohols by nitrous and nitric acid in sulfuric acid media. The oxidation by nitrous acid is rapid and has an activation energy of 10.6 ± 0.8 kcal mol-1. A Hammett plot of logk2 vs. σ+ is linear with a ρ value of -1.4. The oxidation by nitric acid in sulfuric acid media is autocatalytic. From the kinetic and product analyses, it is concluded that a common oxidant, the nitrosonium ion is involved when either nitrous or nitric acid is used. A mechanism is proposed which involves the abstraction of hydride from the alcohols as the rate determining step. It is demonstrated that the autoxidation of the alcohols is catalyzed by nitrous acid or nitric oxide.

Notes: The kinetics of the reaction between nitric oxide and chlorine have been investigated in both carbon tetrachloride and glacial acetic acid. The nitric oxide-oxygen reaction has been investigated in carbon tetrachloride.The appearance of product, NOCl or NO2, was monitored spectrophotometrically at a wavelength of 475 nm for NOCl and 343 nm for NO2. These measurements were performed using an Amino-Morrow stopped-flow apparatus equipped with a Beckman D U monochromator.The data for both the NO—Cl2 and NO—O2 systems could be fitted to the third-order integrated equation and the calculated rate constants were 2.75 × 103 M-2 s-1 and 2.79 × 106 M2 s-1, respectively, at 25.1°C.There was a noted increase in rate constants on changing the solvent from carbon tetrachloride to acetic acid.The likelihood of a termolecular encounter is inherent in the mechanism, however, no real evidence to substantiate either a direct termolecular or a series of two bimolecular steps has been obtained, although a -7 kcal for ΔH0 would support the latter.

Notes: The thermal addition of CF3O3CF3(T) to CF2CCl2(E) has been investigated between 49.6 and 69.5°C. The initial pressure of CF3O3CF3 was varied between 7 and 240 torr and that of CF2CCl2 between 4 and 600 torr. Four products of formula CF3O(E)j OOCF3, where j = 1 → 4 are formed. The sum of the products Σi = 14 CF3O(E)jOOCF3 is equal to the amount of trioxide decomposed.The reaction is homogeneous. Its rate is not affected by the total pressure and the presence of inert gas. It is a free radical telomerization with four basic steps: thermal decomposition of CF3O3CF3 into CF3O. and CF3O2., chain initiation by addition of CF3O. to olefin incorporated in, and telomeric radicals termination.The consumption of alkene is well represented by the equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ - d[E]/dt = k_1 [T]\left\{ {1 + \sum\limits_{j = 1}^3 {\prod\limits_{i = 1}^j {[1 + (k_{t_1 } k_1^{1/2} /k_{gi} } k_t^{1/2})([T]^{1/2} /[E])]^{ - 1} } } \right\} $$\end{document} where (d[E]/d[T]) = \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar n $$\end{document} is the mean chain length of telomerization. \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar n $$\end{document} varies from 1.45 at 1.5 torr of E to 3.3 at 400 torr of E. Above this pressure E has no influence on \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar n $$\end{document}.The estimated value of the constant for the addition of telomeric radicals to alkene is:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_g \simeq 8.6 \pm 6.0 \times 10^4 \exp ( - 2300 \pm 200{\rm col mol}^{{\rm - 1}} /RT){\rm M}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document}

Notes: Gas-phase rate constants for the reaction of NO2 with 16 conjugated olefins were determined at room temperature by either conventional methods for bimolecular processes or by competitive reactions. It was found that the rate constants for conjugated olefins were larger than those for simple mono-olefins by factors of 103-104. Temperature dependence studies reveal that the difference in the rate constants for the two types of reactions can primarily be attributed to differences in their activation energies: k1,3-cyclohexadiene = 5.8 × 10-14 exp[-(6.1 ± 1.6)/RT] cm3 molecule-1 s-1; kcis-2-butene = 4.68 × 10-14 exp(-11.2/RT) cm3 molecule-1 s-1 [2]. A linear free energy relationship between the reactions of OH and NO2 with conjugated diolefins was observed.

Notes: The experimental data for the reactions of oxygen atoms with methane, ethane, and neopentane at temperatures below ca. 600 K have been reexamined. In the case of CH4 and C2H6 reactions, detailed computer models have been assembled to test the assumptions regarding stoichiometries that were made in the original studies in order to derive elementary rate coefficients from the experimentally observed reaction rates. It was found in both cases that the measurements are especially sensitive to secondary reactions not taken into account and impurities in the reagent alkane. Because the original reports did not include sufficient experimental details, it is not now possible to correct their results quantitatively. However, it appears, qualitatively, that the values for the O + CH4 and O + C2H6 rate coefficients were overestimated by factors of approximately 2 to 3 in the 250-400 K temperature range, with the error increasing as T decreases. Although the experimental results for the O + neopentane reaction are not as sensitive to the same kinds of complications, a comparison of the low-temperature measurements with those for the O + ethane reaction suggests that the previously recommended rate coefficients, based on the data of Herron and Huie, are probably also too high by a factor of 2 to 3.

Notes: Rate constants of various simultaneous reactions of t-butoxicarbonyl and t-butyl radicals generated by photolysis of t-butylpivalate in n-heptane are directly determined by kinetic electron spin resonance. The temperature dependence of the decarboxylation reaction t-BuOĊO → t-Bu. + CO2 obeys log )K/S-1( = 13.8-49.0/θ where θ = 2.303 RT/kJ . mol-1. The self- and cross-termination of the radicals are diffusion limited.

Notes: The hydrolysis kinetics of CICN have been reinvestigated from pH 0.0-10.5 and from 18-40°C. In the pH range from 1-5, the hydrolysis rate is invariant and the activation parameters (ΔH

Notes: Study of the thermal decomposition of propane at very low conversions in the temperature range 760-830 K led to refinement of the mechanism of the reaction.The quotient VCH4 + C2H4/VH2 + C3H6 characterizing the two decomposition routes connected with the 1- and 2-propyl radicals proved to depend linearly on the initial propane concentration. This suggested the occurrence of intermolecular radical isomerization: in competition with decomposition of the 2-propyl radical: The linearity led to the conclusion that the selectivity of H-abstraction from the methyl and methylene groups by the methyl radical is practically the same as that by the H atom. The temperature-dependence of this selectivity ( μ = kCH3/kCH2) was given by\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \mu = }\frac{{k_3 }}{{k_4 }} = \frac{{k_1 }}{{k_2 }} = 10^{0.26 \pm 0.03} \exp ( - 7.24 \pm 0.45{\rm kJ mol}^{{\rm - 1}} /RT). $$\end{document} Further evaluation of the dependence gave the Arrhenius representation \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{k_7 }}{{k_6 }} = 10^{ - 5.97 \pm 0.03} \exp (115 \pm 5.1{\rm kJ mol}^{{\rm - 1}} /RT){\rm mol}^{{\rm - 1}} {\rm dm}^{\rm 3} $$\end{document} for the ratio of the rate coefficients of the above isomerization and decomposition reactions.Steady-state treatment resulted in the rate equation of the process, comparison of which with measurements gave further Arrhenius dependences.

Notes: The hydrogen abstraction reactions of tert-butoxyl with germane, phosphine, and trimethylsilane were studied by pyrolyzing di-t-butyl peroxide in the temperature range of 403 to 458 K. From the reported rate constant for the tert-butoxy radical decomposition in the literature, the absolute rate constants were determined from the study of competitive reaction between t-butoxy radical decomposition \documentclass{article}\pagestyle{empty}\begin{document}$$ (t - {\rm BuO }\;{\hbox to 45pt{\rightarrowfill}} {\hskip-42pt ^{{\rm decompose}}}{\hskip1em} {\rm CH}_{\rm 3} {\rm COCH}_{\rm 3} + {\rm CH}_{\rm 3}) $$\end{document} and hydrogen abstraction reaction. (t-BuO + RH → t-BuOH + R, where RH = GeH4, PH3, and HSiMe3)The Arrhenius parameters are found to be as follows: TextEa(kcal mol-1)Log A(1.mol-1s-1)t-BuO + SiHMe32.18.5t-BuO + GeH41.99.1t-BuO + PH31.49.0

Notes: The rate of decomposition of 2-pentoxy radical to acetaldehyde and n-propyl radical has been studied in the presence of NO in competition with nitrite formation at and above 200 kPa pressure over the temperature range of 363-413 K. The rate coefficient for the decomposition is given as log(kla/s-1) = (14.2 ± 0.4) - (13.8 ± 0.8) kcal mol-1/RT ln 10. Isomerization of 2-pentoxy radical by 1,5-hydrogen shift has been investigated in the range 279-385 K in competition with the decomposition in a static system, with methyl radicals present in high concentration to ensure trapping of the isomerized free radicals. The rate coefficient for isomerization is given as log(k3/s-1) = (11.1 ± 0.7) - (9.5 ± 1.1) kcal mol-1/RT ln 10. The implications of the results for atmospheric chemistry are discussed.

Notes: Using a relative rate technique, rate constants for the gas-phase reactions of the OH radical with a series of monoterpenes have been determined in one atmosphere of air at 294 ± 1 K. Relative to a rate constant for the reaction of OH radicals with 2,3-dimethyl-2-butene of 1.12 × 10-10 cm3 molecule-1 sec-1, the rate constants obtained were (in units of 10-11 cm3 molecule-1 sec-1): α-Pinene, 5.45 ± 0.32; β-pinene, 7.95 ± 0.52; Δ3-carene, 8.70 ± 0.43; d-limonene, 16.9 ± 0.5; α-terpinene, 36.0 ± 4.0; γ-terpinene, 17.6 ± 1.8; α-phellandrene, 31.0 ± 7.1; myrcene, 21.3 ± 1.6; and ocimene (acis-, trans-mixture), 25.0 ± 1.9. These are the first quantitative kinetic data reported for many of these monoterpenes. The rate constants obtained are compared with the available literature data and with a priori estimates based on the number and configuration of substituents around the double bond(s). The tropospheric lifetimes of these monoterpenes with OH radicals, NO3 radicals and O3 are estimated and compared. Atmospheric lifetimes with respect to reaction with the OH radical are calculated to range from ∼0.75 hr for α-terpinene to ∼5 hr for α-pinene.

Notes: The kinetics of the oxidation of S2O32- by ClO2- have been studied in aqueous alkaline solution at 900C using classical titrimetric methods to follow the course of the reaction. The reaction takes place according to the stoichiometry S2O32- + 2ClO2- + 2OH- = 2SO42- + 2Cl- + H2O even in large S2O32- excess. There is some indication of a complex reaction pattern, but 70% of the ClO2- disappearance can be best described by the autocatalytic rate equation -d[ClO2-]/dt = k[S2O32-] [ClO2-] [H+] with k = (1.3 ± 0.2) ×108 M-2 sec-1. The mechanism is explained by postulating nucleophilic attack of S2O32- on HClO2 to form a chlorine-containing intermediate.

Notes: Infrared multiple photon decompositions (IRMPD) with more than one reactive pathway can provide significantly more kinetic information than can single-channel photolyses. The rates of the competing unimolecular reactions and the rate of photon absorption are interrelated, so that knowledge of one yields information about the others. The goals and pitfalls of IRMPD experiments on several well-studied classes of reactants are reviewed.

Notes: The rate of the gas phase reaction of hydroxyl radical with methyl nitrate has been measured to be (3.4 ± 0.4) × 10-14 cm3 molecule-1 s-1 at 298 K using flow discharge/ resonance fluorescence techniques. By means of correlation methods, this rate determination is used to predict a vertical ionization potential of 12.6 eV, a bond dissociation energy for H—CH2ONO2 of 101 kcal mol-1, and a rate for O(3P) reaction with methyl nitrate of ca. 9 × 10-17 cm3 molecule-1 s-1. In conjunction with previously derived relative data for reaction of alkyl nitrates with OH radical in the gas phase, a priori estimated reactivities for 1-, 2-, and 3-positionally substituted straight chain alkyl nitrates have been reexamined. Revised reactivities for OH abstraction of specific hydrogens substituted on straight chain alkyl nitrates are presented and discussed, and an atmospheric lifetime of ca. 2 yrs is estimated for methyl nitrate removal due to OH.

Notes: Absolute rate constants for the gas phase reaction of OH radicals with pyrrole (k1) and thiophene (k2) have been measured over the temperature ranges 298-440 and 274-382 K, respectively, using the flash photolysis-resonance fluorescence technique. The rate constants obtained were independent of the total pressure of argon diluent over the range 25-100 torr andwere fit by the Arrhenius expressions \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (2.7 \pm _{0.6} ^{0.8}) \times 10^{ - 11} \exp [(403 \pm 93)/T]{\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = (1.2_{ - 0.6} ^{ + 1.0}) \times 10^{ - 12} \exp [(584 \pm 217)/]{\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document} with rate constants at 298 ± 2 K of k1 = (1.03 ± 0.06) × 10-10 cm3 molecule-1 s-1 and k2 = (8.9 ± 0.7) × 10-12 cm3 molecule-1 s-1. [These errors represent two standard deviations (systematic errors could constitute an additional ca. 10% uncertainty)]. These results are discussed with respect to the previous literature data and the atmospheric lifetimes of pyrrole and thiophene.

Notes: The thermal reactions of endo- and exo-5-Y bicyclo[2.2.2]oct-2-enes (NYBO and XYBO) where Y = methyl, ethyl, and isopropyl have been studied in the gas phase between 567 and 695 K. For both isomers they are parallel first-order retro-Diels-Alder reactions with elimination of ethene (E) and monosubstituted ethene (YE).The observed Arrhenius parameters are used to discuss the mechanism and to estimate the heats of formation and the entropies of NYBO and XYBO. Group values are proposed for estimation of these thermochemical data for compounds of the same type by means of the methods of Benson.

Notes: The kinetics of the gas-phase reactions of naphthalene, 2-methylnaphthalene, and 2,3-dimethylnaphthalene with O3 and with OH radicals have been studied at 295 ± 1 K in one atmosphere of air. Upper limit rate constants for the O3 reactions of 〈3 × 10-19, 〈4 × 10-19, and 〈4 × 10-19 cm3 molecule-1 s-1 were obtained for naphthalene, 2-methylnaphthalene, and 2,3-dimethylnaphthalene, respectively. For the OH radical reactions, rate constants of (in units of 10-11 cm3 molecule-1 s-1) 2.59 ± 0.24, 5.23 ± 0.42, and 7.68 ± 0.48 were determined for naphthalene, 2±methylnaphthalene, and 2,3-dimethylnaphthalene, respectively. These data show that under atmospheric conditions these naphthalenes will react mainly with the OH radical, with life-times due to this reaction ranging from ca. 11 h for naphthalene to ca. 4 h for 2,3-dimethylnaphthalene.

Notes: Unimolecular reactions of mutual isomerization of cyclopentyl and 1-penten-5-yl radicals have been investigated by chemical activation. The radicals were generated by adding energized hydrogen atoms (EH about 23 kcal mol-1) to the double bond of either cyclopentane or 1,4-pentadiene. Based on the extensive steady-state RRKM calculations employing the experimental data from this work as well as from the literature, the threshold energies for the cyclopentyl ring opening and closure are 32 ± 0.3 and 16.2 ± 0.3 kcal mol-1, respectively. The entropy of activation for the ring opening is close to zero.

Notes: Gaseous haloalkyl radicals were prepared by the photolysis of iodohaloalkanes in Pyrex vessels containing mercury (I) halides. Cleavage of the carbon-iodine bond gave mercury (II) halide and a radical which was subsequently shown to react on the ground state electronic energy surface. The usefulness of this method for chemical activation rate constant studies is illustrated by measurement of unimolecular rate constants for decomposition of CH2ClCH2Cl and CF3CH3. Possible mechanisms for photodecomposition of iodoalkanes in the presence of mercury (I) halides are discussed.

Notes: The stopped-flow technique has been used to study the effect of cationic (CTAN), nonionic (Triton X-100), andanionic (SDS) micelles on the rate of the reaction between nickel(II) ion and the ligand pyridine-2-azo-p-dimethylaniline (PADA) at 20.0°C and ionic strength 0.03 mol dm-3. The complex formation reaction is markedly inhibited by both CTAN and Triton X-100 micelles. The kinetic dataare found to conform to a reaction mechanism which implies only partitioning of the ligand between water and the micellar phase, the estimated bindingconstant of PADA being significantly larger in the presence of CTAN aggregates. Anionic micelles strongly speed the complexation reaction, Which occurs in the micellar phase with the same rate and the same mechanism as in water. The extent of binding of PADA to anionic micelles is similar to that found for the cationic micellar aggregates.

Notes: Rate constants have been determined at (298 ± 4) K for the reactions: and the relaxation processes: Time-resolved HF(1,0) emission was observed following the photolysis of F2 with pulses from an excimer laser operating on XeCl (λ = 308 nm). Analysis of the emission traces gave first-order constants for reaction and relaxation, and their dependence on [H2O] and [HCN] yielded: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1{\rm a}} = (1.3 \pm 0.1) \times 10^{ - 11} {\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} s^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1{\rm b}} = (1.3 \pm 0.1) \times 10^{ - 10} {\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} s^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{2{\rm a}} = (3.7 \pm 0.4) \times 10^{ - 13} {\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} s^{ - 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{2{\rm b}} = (3.4 \pm 0.2) \times 10^{ - 12} {\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} s^{ - 1} $$\end{document}

Notes: Translationally hot (3.7 eV center-of-mass collision energy) D atoms can be produced by the dissociative recombinationsof DCO+ ions with electrons in interstellar clouds. The reactions of hot D atoms with H2 molecules is an important factor in determining the D to H abundance ratio in the universe from observations of deuterated species in dense interstellar clouds. A simulation of this reaction has been carried out using exact quasiclassical reaction cross sections, together with a series of approximate total collision cross sections. It was found that the total probability of reaction, PR, at 3.7 eV was approximately 0.4. A reaction probability of this magnitude suggeststhat the loss of D atoms by the title reaction be considered in astrochemical modeling of deuterated molecules.

Notes: In this article we present the results of converged quantum reactivescattering calculations of thermal rate constants for H + H2 using the Liu-Siegbahn-Truhlar-Horowitz (LSTH) potential energy surface. These calculations are based on the coupled states (CS) approximation wherein rotational states having different body fixed angular momentum projection quantum numbers are decoupled. By comparision with accurate coupled channel results on the Porter-Karplus No. 2 (PK2) potential surface, we estimate that the maximumerror in thermal rate constants arising from both this approximation and from other numerical approximations in the calculation is less than 25%. We also show that the sum over projection quantum numbers Ω associated with the CS calculation may be approximated quite accurately in terms of the Ω = 0 rate constants by assuming that the |Ω| 〉 0 rate constants differ from Ω = 0 by a shift in activation energy, which reflects the vibrationally adiabatic bending energy associated with each Ω.Comparison of the LSTH rate constants with experiment indicates average errors of 16% and 24% relative to the two modern measurementsof the rate constants for H + H2. These errors are reduced to 18% and 9% if the CS rate constants are multiplied by exp(0.0065 eV/kT). The expected error (based on recent quantum structure calculations) associated with the 0.425 eV barrier of theLSTH potential surface is 0.0065 eV. Overall, the agreement of either the LSTH or modified LSTH rate constants with experiment is within the 32% maximum disagreement between the two experimental measurements at all butthe lowest temperature that has been studied.Comparison of our CS rate constants with the results from simpler theories is considered using both the LSTH and PK2 potential surfaces. The best overall agreement is with transition state theories that use accurate dynamical methods to calculate tunnelling factors. These include reduced dimensionality quantum dynamics methods and variational transition state theory using either the Marcus-Coltrin or least action ground-state tunnelling paths. Comparison with the results of quasiclassical trajectory calculations indicates substantial errors at low temperatures.

Notes: We present calculations of the rate constants for the title reactions on a new accurate potential energy surface with a 9.65 kcal mol-1 barrier and a carefully fitted long-range attraction. The low-temperature thermal rate constant decreases from the previously calculated value, corresponding to a surface with a barrier of 9.80 kcal mol-1, which is opposite to the direction of change expectedbecause of the change in barrier height. This demonstrates the sensitivity of tunneling contributions to more global characteristics of the surface. The excited-state (n = 1) rate constants alsochange slightly, but not nearly enough to settle the controversial disagreement of theory with experiment for these rate constants.

Notes: The barrier for the hydrogen exchange reaction increases with the bend angle of H3. The implications for the dynamics of the reaction are explored on two levels. The static one uses the concept of a relaxed potential. This provides for a convenient, yet realistic representation. Itallows for the response of the molecule to the approaching atom. Among features made very evident by the relaxed potential is the possibility that hotH atoms can react by insertion. It also shows the widening of the cone of acceptance upon reagent vibrational excitation. On the dynamical level, classical trajectory computations are used to illustrate the dependence of the reactivity on the angle of attack and on the translational and vibrational excitation of the reagents. Detailed product distributions are generally not sensitive to the attack angle. An exception is the HD/H2 branching ratio in H + HD reactive collisions.

Notes: The microcanonical variational transition states of the isotopic reactions H + T2 and T + H2 are shown to migrate with increasing energy in opposite directions away from the classical barrier, i.e., into the reactant and product valleys, respectively. The energy dependence of this isotopic shift is examined and excitation functions are reported, both for collinear and near-collinear reactions.

Notes: The rate constant of the reaction between OH and OCS in helium over the temperature range 255-483 K has been determined using the discharge flow-resonance fluorescence technique. The OCS has been carefully purified to avoid interference from H2S and CO impurities. An FTIR with a multireflection cell was used to determine the impurity concentrations and the purified sample was found to contain less than 0.005% of H2S. At 300 K, the rate constant was determined to be (2.0 ±0.40.8) × 10-15 cm3 molecule-1 s-1. Although the rate constants showed slight positive deviation at lower temperatures, thev can be satisfactorily fitted by the Arrhenius equation, k = 1.13 × 10-13 exp(-1200/T) cm3 molecule-1 s-1. No pressure dependence was observed at all temperatures, nor was O2 enhancement observed under our experimental conditions.

Notes: The thermal decomposition of ethylbenzene has been investigated behind reflected shock waves over the temperature and pressure ranges of 1350-2080 K and 0.25-0.5 atm using a 1.6% C8H10 — Ne mixture. Major products of the pyrolysis are C7H8, C7H7, C6H6, C4H2, C2H4, C2H2, and CH4; C8H8 appears throughout the temperature range as a minor product. Comparison of the product profiles obtained by time-of-flight mass spectrometry and the results of model calculations strongly supports the initiation step of β C—C bond homolysis for C8H10 dissociation. A 51 kinetic step reaction mechanism with 24 species was formulated to model the temperature and time dependence of the major products observed in our experiments.

Notes: Ozone, O3, reacts with a carbon sample at room temperature. Clean carbon samples show a half to one and a half order of magnitude increased initial rate constant (k0) for O3 loss relative to repetitively exposed carbon samples. The ozone loss rate and therefore the rate constant reaches steady state (kss) on the time scale of tens of minutes, upon exposure to a characteristic dose of 8 × 1017 molecules for a 30-mg carbon sample independent of the flow rate. This characteristic dose closely corresponds to a monolayer of adsorbed ozone molecules on the carbon sample. Both k0 and kss decrease with increasing flow rate of O3 into the reactor, and the loss rate is found to depend on [O3]. When the loss rate is plotted against the steady state concentration of O3, a saturation plot results which is proportional to the surface coverage, θ, at a given [O3].This interpretation rests upon a Langmuir type kinetics model with an assumed first-order dependence of the loss rate constant. The “sticking coefficients” track the rate constants and are on the order of 10-3 to 10-5 depending on the carbon sample, dose, and flow rate. Furthermore, ko depends on the length of the dark period (absence of O3 exposure) and is larger the longer time the sample has had to recuperate from previous O3 exposures up to a period of 150 s. This surface relaxation is thought of as a time-dependent change in surface coverage taking place in the dark period and is therefore an indication of a slow surface diffusion/reaction that can be separated from the adsorption-desorption kinetics. The mass balance shows that for every ozone molecule that is lost on the surface, an oxygen molecule is found. This adsorbed odd oxygen is then responsible for product formation, which comprises the volatile components CO and CO2 to an extent of 20 to 40% of the odd oxygen deposited on the surface. The difference is thought to be in a preoxidized state on the carbon sample, which evolves CO and CO2 upon heat treatment.

Notes: The kinetics of four gas-phase reactions involving halogenated methyl radicals (R = CF3, CF2Cl, CFCI2, and CCI3) with molecular chlorine have been studied using a tubular reactor coupled to a photoionization mass spectrometer. The radicals were homogeneously generated by the pulsed photolysis of precursor molecules at 193 nm. The subsequent decays of the radical concentration were monitored in real-time experiments as a function of Cl2 concentration to obtain the rate constants of these R + Cl2 reactions. Where possible, the rate constants were measured as a function of temperature to determine Arrhenius parameters. Apparent discrepancies between these measured rate constants for CF3 and CCl3 with Cl2 and ones obtained in prior indirect studies are explained. The higher activation energies for these R + Cl2 reactions compared to that of the CH3 + Cl2 reaction are attributed in part to the different polarities of the transition states formed.

Notes: The unimolecular decomposition of 2,2 dimethyloxetance to give either isobutence and formaldehyde or ethene and acetone induced by a pulsed CO2 laser has been investigated. Absorption characteristics and fractional decomposition have been studied as a function of laser fluence, irradiation frequency, reactant pressure, and added inert bath gas. Both absorption cross section and fractional decomposition are approximately independent of pressure of 2,2-dimethyloxetane below 50 times; 10-3 torr and increase with pressure at higher pressures of 2,2-dimethyloxetane. At pressures sufficiently low that collisions are negligible during the laser pulse, added inert gases reduce the amount of decomposition. Calculations of the fractional decomposition have been carried out based on RRKM theory and assuming either a Boltzmann or a Poisson intermolecular energy distribution. Master equation calculations of both absorption and decomposition for 10R20 irradiation have also been performed. Agreement between observed and calculated results for 10R20 irradiation could be obtained only by assuming that most, but not all, of the molecules in the irradiated volume absorb the laser radiation. Differences between the absorptions of the 10R20 and 9P20 lines and in the resulting extents of decomposition indicate that the fraction of irradiated molecules which absorbs 9P20 radiation is smaller than the fraction which absorbs 10R20 radiation.

Notes: A test of the Kassel quantum expressions for unimolecular rate constants and densities of vibrational states is described. Rate constants are calculated for nine reactions previously used in such tests, over a wide range of temperatures and pressures. The Kassel expression using the geometric mean of the molecular vibration frequencies is generally found to give better results than that using the arithmetic mean.

Notes: Hydrogen abstraction by 1-phenylethyl radicals (ṘH) from phenylmethyl-carbinol (HROH) and benzyl alcohol (H2R′OH) has been studied in the liquid phase at 120°C. 1-Phenylethyl radicals have been generated by thermal decomposition of azo-bis-1-phenyl ethane and the formation of ethylbenzene (RH2), acetophenone (RO), and 2,3-di-phenyl butane (R2H2) has been monitored during the reaction.In order to optimize the experimental conditions, a mechanism has been assumed for the various pathways of the disappearance of ṘH and by using estimated rate parameters a presimulation was performed.The relative rate constants obtained are: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\frac{{k_{\rm H} }}{{\sqrt {{\rm 2}k_t } }} = 1.4{\rm } \times {\rm }10^{ - 4} {\rm L}^{1/2} {\rm mol}^{ - 1/2} {\rm s}^{ - 1/2} } & {{\rm for}} & {{\rm HROH}} \\ \end{array} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\frac{{k_{\rm H} }}{{\sqrt {{\rm 2}k_t } }} = 1.0{\rm } \times {\rm }10^{ - 4} {\rm L}^{1/2} {\rm mol}^{ - 1/2} {\rm s}^{ - 1/2} } & {{\rm for}} & {{\rm H}_{\rm 2} {\rm R'OH}} \\ \end{array} $$\end{document} where kH refers to the hydrogen abstraction while kt is the combination rate coefficient of the radicals ṘH.

Notes: Conventional transition-state theory is used for extrapolating rate coefficients for reactions of O atoms with alkanes to temperatures above the range of experimental data. Expressions are developed for estimating structural properties of the activated complex necessary for calculating enthalpies and entropies of activation. Particular attention is given to the problem of the effect of the O atom adduct on the internal rotations in the activated complex. Differences between primary, secondary, and tertiary attack are discussed, and the validity of representing the activated complexes of all O + alkane reactions by a fixed set of vibrational frequencies and other internal modes is evaluated. Experimental data for reactions of O atoms with 15 different alkanes (CH4, C2H6, C3H8, C4H10, C5H12, C6H14, C7H16, C8H18, i-C4H10, (CH3)4C, (CH3)2CHCH(CH3)2, (CH3)3CC(CH3)3, c-C5H10, c-C6H12, c-C7H14) are reviewed.The following approximate expressions for ΔS

Notes: A new technique is described for quantitative measurement of the conditions of reactant concentration at ignition in mixtures of carbon monoxide and oxygen. A thin film of carbon covering the surface of a quartz reaction vessel reacted with oxygen to form carbon monoxide and small quantities of water. Explosions were observed above 900 K over the pressure range 15-100 torr with ratios of CO/O2 far below those hitherto explored. The onset of explosion was favored by the addition of hydrogen, methane, and water and was inhibited by the addition of inert gases. A simple mechanism predicts the occurrence of an explosion over a wide range of product composition and total pressure.

Notes: The kinetics of the solvolysis of the ion trans-[Coen2N3Cl]+ have been investigated at several temperatures in mixtures of water with t-butyl alcohol with concentrations of the latter ranging up to 50 vol% or a mol fraction of 0.16. Values for the enthalpy and entropy of activation show sharp changes with changing solvent composition which can be correlated with extrema in the physical properties of the mixture concerned with sharp changes in solvent structure. Plots of log(rate constant) against the reciprocal of the dielectric constant and against the Grunwald-Winstein Y factor are both curved. The application of a free energy cycle shows that the effect of changes in solvent structure on the solvolysis dominates on the cobalt(III) cation in the transition state over that on the cation in the initial state.

Notes: Conditions of applicability of quasi-steady-state kinetic treatment have been investigated with respect to the explanation of the decomposition of propane and the influence of ethylene on this.From the measured rate of accumulation of ethane and from the relations between the kinetic equations describing product formation, the rate parameters of the initiation reactions were determined, for which the temperature-dependences \documentclass{article}\pagestyle{empty}\begin{document}$$ k_i = 10^{17,05 \pm 0.99} \exp ( - 356 \pm 11{\rm kJmol}^{{\rm - 1}} /RT)s^{ - 1} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{ie} = 10^{12.0 \pm 0.99} \exp ( - 225 \pm 15{\rm kJmol}^{{\rm - 1}} /RT){\rm mol}^{{\rm - 1}} {\rm dm}^{\rm 3} s^{ - 1} $$\end{document} were found.In the decomposition of propane under the examined conditions, the chain length exceeds 500. In response to ethylene the chain length significantly decreases, but even in this case the decomposition chains are long enough for it to be assumed that the ratios of radical concentrations are governed by the propagation steps.Calculations demonstrated that the actual radical concentration during a sufficiently short induction period approximates to the stationary concentration, so that it does not seriously affect the accuracy of the kinetic treatment.

Notes: The thermal decomposition of butene-2-cis at low conversion and its effect on the pyrolysis of propane have been studied in the temperature range 779-812 K.It was established that 2-butene decomposes in a long-chain process, with the chain cycle \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - C}_{\rm 4} {\rm H}_{\rm 8} + {}^.{\rm CH}_{\rm 3} \to {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 7} + {\rm CH}_{\rm 4} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - C}_{\rm 4} {\rm H}_{\rm 8} + {}^.{\rm CH}_{\rm 3} \to {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 7} + {\rm CH}_{\rm 4} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - C}_{\rm 4} {\rm H}_{\rm 8} + {}^.{\rm CH}_{\rm 3} \to {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 7} + {\rm CH}_{\rm 4} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 7} \to {}^.{\rm H} + 1,3 - {\rm C}_{\rm 4} {\rm H}_{\rm 6} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - C}_{\rm 4} {\rm H}_{\rm 8} + {}^.{\rm H} \to {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 7} + {\rm H}_{\rm 2} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \to 2 - {\rm \dot C}_{\rm 4} {\rm H}_{\rm 9} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - C}_{\rm 4} {\rm H}_{\rm 8} \to + 1,3 - {\rm C}_{\rm 3} {\rm H}_{\rm 6} + {\rm H}_{\rm 2} $$\end{document}(Besides the radical path, the molecular reaction can also play a role in the formation of the products.)The thermal decomposition of propane is considerably inhibited by 2-butene, which can be explained by the fact that the less reactive radicals formed in the reactions between the olefin and the chain-carrying radicals regenerate the chain cycle more slowly than the original radicals in the above chain cycle or in the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm C}_{\rm 3} {\rm H}_{\rm 8} + {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 7} \to 1 - {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} + {\rm C}_{\rm 4} {\rm H}_{\rm 8} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \to 2 - {\rm \dot C}_{\rm 4} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 8} $$\end{document}The reactions of the 2-propyl radical \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - \dot C}_{\rm 3} {\rm H}_{\rm 7} + 2 - {\rm C}_{\rm 4} {\rm H}_{\rm 8} \to {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 7} + {\rm C}_{\rm 3} {\rm H}_{\rm 8} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \to 2 - {\rm \dot C}_{\rm 4} {\rm H}_{\rm 9} + {\rm C}_{\rm 3} {\rm H}_{\rm 6} $$\end{document} are further initiation steps. The ratios of the rate coefficients of the elementary steps of the decomposition (Table III) have been determined via the ratios of the products.Estimation of the radical concentrations indicated that only the methyl, 2-propyl and methylallyl radicals are of importance in the chain termination.On the basis of the inhibition-influenced curves, the role of the bimolecular initiation steps. \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - C}_{\rm 4} {\rm H}_{\rm 8} + {\rm C}_{\rm 3} {\rm H}_{\rm 8} \to {\rm \dot C}_{\rm 4} {\rm H}_{\rm 9} + {\rm \dot C}_{\rm 3} {\rm H}_{\rm 7} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2 - C}_{\rm 4} {\rm H}_{\rm 8} + 2 - {\rm C}_{\rm 4} {\rm H}_{\rm 8} \to {}^.{\rm C}_{\rm 4} {\rm H}_{\rm 9} + {\rm C}_{\rm 4} {\rm H}_{\rm 7} $$\end{document} could be clarified in the presence of 2-butene.

Notes: The pyrolysis of ethylbenzene has been investigated in shock waves with the laser schlieren technique. Mixtures of 1 and 2% ethylbenzene in krypton were studied for reaction conditions of 1300-1800 K, 70-550 torr. At high temperatures, the initial rapid endothermic dissociation is followed by a region of net exothermic reaction, which is readily understood as arising mainly from methyl radical recombination after dissociation to methyl and benzyl radicals. The initial unimolecular dissociation rates show no detectable dependence on pressure; with ΔH0298 = 75.7 kcal mol-1 these rates are \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k({\rm s}^{{\rm - 1}}) = 13.49 - 60.0/\theta $$\end{document} An RRKM extrapolation suggests \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_\infty ({\rm s}^{{\rm - 1}}) = (15.95 \pm 0.3) - (74.7 \pm 2)/\theta $$\end{document} in excellent agreement with previous lower temperature data.

Notes: The hydrogen transfer reaction between C2H6 and CF3 radicals, generated by the photolysis of CF3I, has been studied in the temperature range 298-617 K. The rate constant, based on the value of 1013.36 cm3 mol-1 s-1 for the recombination of CF3 radicals, is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_2 = (11.90 \pm 0.09) - (33230 \pm 740)/19.145T $$\end{document} where k2 is in cm3 mol-1 s-1 and E is in J mol-1. These results are compared with those previously reported, and the following best value for k2 is recommended: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_2 = (11.94 \pm 0.07) - (33670 \pm 540)/19.145T $$\end{document}

Notes: The reaction kinetics of carbon dioxide with four alkanolamines of industrial importance (MEA, DGA, DEA, and DIPA) have been investigated with the aid of the stopped-flow technique, allowing the determination of rate constants for carbamates formation. The constants obtained for MEA at 20°C and 25°C are in good agreement with recent literature data. The kinetic behavior of DGA was found to be almost identical to that of MEA.The rate constants obtained for DIPA at 25°C (54 M-1 s-1) is half as large as that for DEA (110 M-1 s-1). The former one is satisfactorily compared with the recent values proposed by Blauwhoff et al. Activation energies have also been obtained for DEA (23.2 kJ mol-1) and for DIPA (58.7 kJ mol-1) and their mechanistic implications are discussed in relation with the relevanceof a rate-determining proton transfer step in the process of carbamate formation.

Notes: The influence of the effective potential energy curves on the calculation of the strong collision limiting low-pressure rate coefficients of thermal dissociation-recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero-point barriers, as originallyproposed by Troe, was performed. A comparison between calculations realizedwith an exactly fitted looseness parameter, α, and with a standard value of α = 1.0 Å-1, indicates that the use of this last value is satisfactorily justified in the evaluation of thestrong collision limiting low-pressure rate coefficients. A study interms of restrictive relationships between the looseness and Morse parameters and ab initio, radial potentials (for CH4, CH3O2, and HO2) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long-range potentials are also briefly discussed.

Notes: The abstraction of hydrogen and deuterium from 1,2-dichloroethane, 1,1,2-trichloroethane, and two of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigatedin the temperature range 0-95°C using methane as a competitor. Rate constants and their temperature coefficients are reported for the following reactions Over the temperature range of this investigation an Arrhenius law temperature dependence was observed in all cases. Based on the adopted rate coefficient for the chlorination of methane [L.F. Keyser, J. Chem. Phys., 69, 214 (1978)] \documentclass{article}\pagestyle{empty}\begin{document}$$ k_r /{\rm cm}^{\rm 3} {\rm s}^{{\rm - 1}} = (1.65 \pm 0.32) \times 10^{ - 11} \exp [ - (1530 \pm 68)/T] $$\end{document} which is commensurate with the present temperature range, the following rate constant values (cm3 s-1) are obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (4.93 \pm 0.96) \times 10^{ - 11} \exp [ - (1087 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = (2.92 \pm 0.57) \times 10^{ - 11} \exp [ - (1362 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 = (2.39 \pm 0.57) \times 10^{ - 11} \exp [ - (1750 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_4 = (1.68 \pm 0.33) \times 10^{ - 11} \exp [ - (1965 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_5 = (1.22 \pm 0.24) \times 10^{ - 11} \exp [ - (1948 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_6 = (1.47 \pm 0.28) \times 10^{ - 11} \exp [ - (1910 \pm 68)/T] $$\end{document} The observed pure primary, and mixed primary plus α- and β3-secondary kinetic isotope effects at 298 K are k3/k6 = 2.73 ± 0.08, and k1/k2 = 4.26 ± 0.12, respectively. Both show a normal temperature dependence decreasing to k3/k6 = 2.39 ± 0.06 and k1/k2 = 3.56 ± 0.09 at 370 K. Contrary to some simple theoretical expectations, the kinetic isotope effect for H/D abstraction decreases with increasing number of chlorine substituents in the geminal group in a parallel manner to the trend established previously for C1-substitution in the adjacent group. The occurrence of a β-secondary isotope effect, k4/k5, is established; this effect suggests a slight inverse temperature dependence.

Notes: Acetylene and vinylacetylene mixtures were pyrolyzed at 400-500°C in the absence and presence of O2 or NO. The major product of the interaction between C2H2 and C4H4 is polymer, but benzene is also produced. Both the C2H2 removal and C6H6 formation rates arefirst-order in C2H2 and C4H4. The rate coefficients are \documentclass{article}\pagestyle{empty}\begin{document}$$ \log (k\{ {\rm C}_{\rm 2} {\rm H}_{\rm 2} \}, M^{ - 1} {\rm s}^{{\rm - 1}}) = 6.26 \pm 0.20 - (70.6 \pm 3.6)/2.3RT $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \log (k\{ {\rm C}_{\rm 6} {\rm H}_{\rm 6} \}, M^{ - 1} {\rm s}^{{\rm - 1}}) = 8.65 \pm 0.39 - (125.9 \pm 5.4)/2.3RT $$\end{document} where R is the ideal gas constant in kJ/mol-K. Benzene formation occurs by two processes: a concerted molecular mechanism (≃60%) and a singlet diradical mechanism (≃40%).

Notes: The rate of decarbonylation of the hydroxyacetyl radical in acetonitrile is measured by effect modulated ESR spectroscopy and found to be log (KD/s-1) = (11.0 ± 1.5)-(2.3RT)-1 (37 ± 8)kJ/mol. The result is shown to be reasonably well connected with a variety of decarbonylation data known for other acyl species by asimple Evans-Polanyi relation.

Notes: An upper limit for the reaction rate of CO with the nitrate radical NO3 has been determined equal to 4 × 10-19 cm+3 molec-1 s-1 at 295 ± 2 K. In the experiment the isotopic species C13O16 and C13O18 mixed at 1-2 ppmv level in synthetic air have been reacted with NO3 and the reaction followed using long path infrared absorption FT spectroscopy. The result is of interest in the studies on the role played by NO3 in nighttime tropospheric chemistry.

Notes: The rate constant k1 for the reaction of OH radicals with CIO2 molecules was measured in a discharge flow system over the temperature range 293 ≤ T ≤ 473 K and at low pressures, 0.5 ≤ P ≤ 1.4 torr, using electron paramagnetic resonance or laser-induced fluorescence to monitor the pseudo first-order decay of OH concentrations. At 293 K, the value obtained for k1 was (7.2 ± 0.5) × 10-12 cm3 molecule-1 s-1. Within the temperature range of this study, a negative temperature dependence was observed: k1 = (4.50 ± 0.75) × 10-13 exp[(804 ± 114)/T] cm3 molecule-1 s-1. HOCl was detected by mass spectrometry as a product of the reaction and was titrated using OH + Cl2 as a source in the calibration experiments. A simulation of the mechanism of the OH + ClO2 reaction indicated that HOCl was mainly produced in the first reaction step. Both this result and the observed T dependence of k1 suggest that this reaction proceeds via an intermediate adduct with a cyclic geometry.

Notes: The pertechnetate ion oxidizes ascorbic acid in strong acid medium to form red species. A reaction mechanism has been developed which correctly predicts all the experimental facts. The results obtained support the postulate according to which the red species corresponds to a complex formed between Tc(V) and dehydroascorbic acid. The rate constants and Arrhenius parameters have been investigated.