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Notes: Since the activation energy for the reaction RH + O2 → R· + HO2. is very close to its endothermicity, the R-H bond energy can be calculated from the activation energy for free radical formation by the reaction RH + O2. The relation between Ei and QR-H was found empirically after measuring Ei by the method of inhibitors for the oxidation of cyclohexane, n—heptane, and toluene: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm Q}_{{\rm R} - {\rm H}} = E_i + 53{\rm kcal/mole}$$\end{document}The values of QR-H are calculated from these and earlier experimental data for five hydrocarbons, five phenols, and four aromatic amines.

Notes: 3,3-Dimethylbutanol-2 (3,3-DMB-ol-2) and 2,3-dimethylbutanol-2 (2,3-DMB-ol-2) have been decomposed in comparative-rate single-pulse shock-tube experiments. The mechanisms of the decompositions are The rate expressions are \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm B} (2,3{\rm - DBM - ol - 2}) = 10^{16.24} {\rm exp}(- 37,400/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm EP} (2,3{\rm - DBM - ol - 2}) = 10^{14.17} {\rm exp}(- 32,300/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm ET} (2,3{\rm - DBM - ol - 2}) = 10^{13.66} {\rm exp}(- 32,700/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm B} (3,3{\rm - DBM - ol - 2}) = 10^{16.33} {\rm exp}(- 37,500/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm EP} (3,3{\rm - DBM - ol - 2}) = 10^{14.0} {\rm exp}(- 34,200/T)\sec ^{- 1}$$\end{document} They lead to D(iC3H7—H) - D((CH3)2(OH) C—H) = 8.3 kJ and D(C2H5—H) - D(CH3(OH) CH—H) = 24.2 kJ.These data, in conjunction with reasonable assumptions, give \documentclass{article}\pagestyle{empty}\begin{document}$$k(t{\rm C}_{\rm 4} {\rm H}_{\rm 9} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm C(CH}_{\rm 3} {\rm)}_{\rm 2} {\rm OH}) = 10^{16.8} {\rm exp}(- 40,900/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k(i{\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm CH(CH}_{\rm 3} {\rm)OH}) = 10^{16.5} {\rm exp}(- 41,100/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k(n{\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm CH}_{\rm 2} {\rm CH}_{\rm 2} {\rm OH}) = 10^{16.2} {\rm exp}(- 41,100/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k({\rm C}_{\rm 2} {\rm H}_{\rm 5} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm CH}_{\rm 2} {\rm OH}) = 10^{16.4} {\rm exp}(- 42,500/T)\sec ^{- 1}$$\end{document}andThe rate expressions for the decomposition of 2,3-DMB-1 and 3,3-DMB-1 are \documentclass{article}\pagestyle{empty}\begin{document}$$ k(2,3{\rm - DMB - 1} \to {\rm CH}_3 \cdot + {\rm H}_2 {\rm C} = {\rm C}({\rm CH}_3 ) - \mathop {\mathop {\rm C}\limits^{\rm .} {\rm H}({\rm CH}_3 )) = 10^{16.0} \exp ( - 35,700/T)\sec ^{ - 1} } $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k(3,3{\rm - DMB - 1} \to {\rm CH}_{\rm 3} \cdot + {\rm H}_2 {\rm C = CH} - \mathop {\rm C}\limits^{\rm .} ({\rm CH}_3 )_2 ) = 10^{16.2} \exp ( - 35,500/T)\sec ^{ - 1} $$\end{document}

Notes: The role of ethenoxy radicals in the pyrolysis of CH3CDO was studied by mass spectrometric analysis of the isotopic composition of the methane, ethane, and recovered aldehyde. Experimental evidence was obtained for the formation of ethenoxy radicals and for their reaction with acetaldehyde.Mixtures of CH3CHO and CH3CDO were pyrolyzed in order to minimize H-D scrambling in the methyl group of the aldehyde. A kinetic treatment of the methyl radical reactions and furnished the rate constant ratios (k2a + k2b)/k1a = 2.7 and k1b/k1a = 0.62 at 785°K. It is concluded that at the usual temperatures of CH3CHO pyrolysis the rate of alkyl hydrogen capture is comparable to that of formyl hydrogen abstraction.The results and conclusions are discussed and compared with previous work.

Notes: The gas-phase photochlorination (λ = 436 nm) of the 1,1,1,2-C2H2Cl4 has been studied in the absence and the presence of oxygen at temperatures between 360 and 420°K. Activation energies have been estimated for the following reaction steps: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm CCl}_3 {\rm CHCl}^{\rm .} + {\rm Cl}_2 \to {\rm CCl}_3 {\rm CHCl}_{\rm 2} + {\rm Cl}^{\rm .}} & {E_3 = (4.6 \pm 0.4){\rm kcal/mole}} \\ \end{array}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm CCl}_3 {\rm CHCl}^{\rm .} \to {\rm CCl}_2 {\rm CHCl} + {\rm Cl}^{\rm .}} & {E_4 = (20.6 \pm 1.4){\rm kcal/mole}} \\ \end{array}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm CCl}_3 {\rm CHClO}_{\rm 2} {\rm CHClCCl}_3 \to 2{\rm CCl}_3 {\rm CHClO}^{\rm .}} & {E_{15} = (33.5 \pm 3.0){\rm kcal/mole}} \\ \end{array}$$\end{document}The dissociation energy D(CCl3CHCl—O2) ± (24.8 ± 1.5) kcal/mole has also been estimated from the difference in activation energy of the direct and reverse reactions The mechanism is discussed and the rate parameters are compared to those obtained for a series of other chlorinated ethanes.

Notes: The rate constant for tert-butyl radical recombination has been measured near 700°K by the very-low-pressure pyrolysis (VLPP) technique and was found to be 108.8±0.3 M-1·sec-1 with neglibible temperature dependence. The thermochemical parameters for tert—butyl radicals were varied within reasonable limits to bring into agreement the data for the decomposition of 2,2,3,3-tetramethyl butane and the recombination of tert-butyl radicals. The revised thermochemistry also makes the gas-phase results and liquid-phase results compatible.

Notes: The rate of CH4 disappearance in a shock-heated CH4:D2:Ar = 9.70:9.86:80.44 mixture was monitored by coincidence absorption of the 2948 cm-1 He-Ne laser line over the shockfront temperature range of 1900-2300K. Comparison with CH4 pyrolysis results by means of computer simulations suggested that atom and free radical chains are responsible for the homogeneous D/H exchange reaction on CH4.Additional simulations for the experimental conditions of previous single-pulse shock tube experiments led to the recognition of a high sensitivity of the exchange rate to trace amounts of hydrocarbon impurity and to the dissociation rate of CH4.

Notes: The flash photolysis of HN3 was studied by coordinated time-resolved spectroscopic measurements of HN3 NH(a1Δ), NH(X3Σ), NH(c1π), NH(A3π), NH2, and N3 following flash photolysis of mixtures of HN3 with argon or helium. The primary photolysis is complex, but when the wavelength distribution of the flash is limited to values greater than about 200 nm, the major reactive product is NH(1Δ), or states which quickly decay to NH(1Δ). Disappearance of NH(1Δ) occurs predominantly by the process \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm NH(}^1 \Delta {\rm)} + {\rm HN}_{\rm 3} \to {\rm NH}_{\rm 2} + {\rm N}_{\rm 3}} & {k_2 = 9.3 \times 10^{- 11} {\rm cm}^{\rm 3} /{\rm mole} \cdot {\rm sec}} \\ \end{array}$$\end{document}The process has little, if any, energy of activation, and no detectable dependence on the pressure of inert gas below 1 atm. The rate of formation of NH2 in its ground vibrational state depends on the inert gas pressure in a way that can be accounted for by vibrational relaxation from initial excited vibrational states. The total amount of NH2 is roughly comparable with the amount of HN3 decomposed by primary photolysis. The observed N3 can be attributed to the NH(1Δ) + HN3 reaction, although a smaller amount could also be formed by primary photolysis. The value of k2 is revised upward from the value given in a preliminary report on the basis of a more careful consideration of the effects of Beer's law failure in absorption measurements involving narrow spectral lines.

Notes: The oxidation of α-hydroxy acids and α-hydroxy ketones by Br(V) follows the rate-law \documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{- d[{\rm Br(V)}]}}{{dt}} = k_2 [{\rm Br(V)}][{\rm substrate}]$$\end{document}However, the former reaction exhibits a second-order dependence on hydrogen ion concentration while the latter reaction has a third-order dependence. A mechanism involving a slow formation of a bromate ester of the α-hydroxy acid followed by a fast decomposition is proposed. A rate-determining formation of a bromate ester from the conjugate acid of benzoin, followed by a rapid decomposition of the bromate ester, explains the kinetic data for the oxidation of benzoin.

Notes: The consumption of nitric oxide in the shock-heated nitric oxide, hydrogen, and argon system had been studied and modeled as the chain-branching process containing the reaction H + NO ⇀ N + OH (k3) as a slow-branching step. Through the computer simulation method the authors clarified the role of the initiation reaction H2 + NO ⇀ HNO + H (k1) in the system and obtained the rate constants of k1 and k3 as k1 = 1013.5±0.15 exp (-55.2 kcal/RT) and k3 = 1013.7±0.15 exp (-48.7 kcal/RT) (cm3/mole·sec), respectively. k1 was one order larger than the value obtained in the flame experiment by Halstead and Jenkins.

Notes: Dichloroethylene (DCE), either cis or trans, was reacted with O3 at 23°C in both N2 and O2 buffered mixtures. Both reactant consumption and product formation were monitored by infrared spectroscopy and, in some cases, O3 consumption was monitored by ultraviolet absorption. For thoroughly dried mixtures, the initial products were only HCClO and O2, but geometrical isomerization also occurred. The stoichiometry of the overall reaction always was The HCClO was unstable and disappeared slowly in a first-order reaction which was, at least in part, heterogeneous. The products were CO and HCl so that the stoichiometric reaction was The rate law was complex. The rate was always faster in N2 than in O2. In the N2 buffered reaction, inhibition occurred as the reaction progressed and O2 was produced. From the reactant and product decay curves, the following rate behavior was established: where high and low concentrations are relative terms for the initial pressure ranges covered ([DCE]0 = 0.21-78.4 torr, [O3]0 = 0.30-6.76 torr). The rate coefficients k2, k3, and k4 were larger for the trans-DCE than the cis-DCE, and for each isomer they were larger in N2 than in O2 buffered reactions.The ozonolysis can be explained in terms of the mechanism where R2 is DCE, RO is HCClO, and RO2 is HCClO2. Rate ceofficients are computed.The isomerization is first order in [O3] and approximately first order in [DCE] for the limited kinetic data we were able to obtain. The isomerization does not appear to be explained by the reverse reactions of reactions (6), (7), and (9). Presumably isomerization occurs through some other route.

Notes: Rate constants for the self-reaction of tertbutyl radicals in six nalkanes are determined as functions of temperature by kinetic electron-spin resonance spectroscopy and from rates of product formation. They are well described by a Smoluchowski-Stokes-Einstein treatment including effects of microfriction and spin statistical factors, indicating complete diffusion control. The ratio of disproportionation to combination products is found to depend on temperature and solvent. This is tentatively ascribed to reorientational effects in the encounter pairs.

Notes: Our earlier work on the formation of particulate NH4NO3 in the NH3—O3 reaction at 25°C is extended to include air as a diluent and H2O vapor as an additive. More extensive data at different values of [NH3]/[O3]0 were obtained also, where [O3]0 is the initial O3 concentration. In our earlier work we concluded that NH4NO3 vapor was dissociated to NH3 + HNO3 and that the HNO3 was removed by diffusion to the walls with a rate coefficient kdiff = 0.4 min-1 or by condensation on the suspended particles. Particles were nucleated by 8 NH3—HNO3 pairs when their concentration product reached 5.8 × 1027 molec2/cm6 with a rate coefficient knucl of 6.2 × 10-224 cm45/min and removed by coagulation with a rate coefficient kcoag of 1.3 × 10-7 cm3/min. A corrected calculation modifies the number of pairs required to 6-7 with a correspondingly changed value of knucl.With the more extensive data of the present study the indications are that the vapor-phase NH4NO3 monomer is not dissociated and that its diffusion constant for loss to the walls varies between 0.3 and 0.9 min-1 for different reaction conditions. Nucleation occurs when the NH4NO3 vapor concentration reaches 1.0 × 1012 molec/cm3 via. \documentclass{article}\pagestyle{empty}\begin{document}$$r{\rm NH}_{\rm 4} {\rm NO}_{\rm 3} (g) \to ({\rm NH}_{\rm 4} {\rm NO}_{\rm 3})_r (s)$$\end{document}where r is 9 and the nucleation rate coefficient knucl is 3 × 10-108 cm24/min. With 5.0 or 9.5 torr of H2O vapor present, there is an excess of particles produced over that expected from this rate coefficient, indicating an additional nucleation step in which H2O vapor participates directly to produce a hydrated salt. The coagulation coefficient of (1.87 ± 0.14) × 10-7 cm3/min found here is in good agreement with that found previously.

Notes: The room temperature reactions between oxygen atoms and methanethiol, ethanethiol, and methylsulfide have been studied in crossed jets to directly detect and identify the free-radical and stable products they produce. Knowledge of the products was used to assign reactive routes. The overall rate constants for all three O-atom reactions were also measured at 300 ± 2°K using a fast-flow reactor. They are 1.9 (CH3SH), 2.8 (C2H5SH), and 63 (CH3SCH3) × 10-12cm3/mol · sec. The identity of the detected products and the trend in rate constants in these reactions support an electrophilic addition mechanism followed by decomposition of the excited adduct by S-R bond cleavage (R = H, CH3, or C2H5).

Notes: By using isobutane (t-BuH) as a radical trapit has been possible to study the initial step in the decomposition of dimethyl peroxide (DMP) over the temperature range of 110-140°C in a static system. For low concentrations of DMP (2.5 × 10-5-10-4M) and high pressures of t-BuH (∼0.9 atm) the first-order homogeneous rate of formation of methanol (MeOH) is a direct measure of reaction (1): \documentclass{article}\pagestyle{empty}\begin{document}${\rm DMP}\mathop \to \limits^1 2{\rm Me}\mathop {\rm O}\limits^{\rm .},{\rm Me}\mathop {\rm O}\limits^{\rm .} + t{\rm - BuH}\mathop \to \limits^4 {\rm MeOH} + t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u}$\end{document}. For complete decomposition of DMP in t-BuH, virtually all of the DMP is converted to MeOH. Thus DMP is a clean thermal source of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}. In the decomposition of pure DMP complications arise due to the H-abstraction reactions of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document} from DMP and the product CH2O. The rate constant for reaction (1) is given by k1 = 1015.5-37.0/θ sec-1, very similar to other dialkyl peroxides. The thermochemistry leads to the result D(MeO—OMe) = 37.6 ± 0.2 kcal/mole and /H°f(Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}) = 3.8 ± 0.2 kcal/mole. It is concluded that D(RO—OR) and D(RO—H) are unaffected by the nature of R. From ΔS°1 and A1, k2 is calculated to be 1010.3±0.5 M-1· sec-1: \documentclass{article}\pagestyle{empty}\begin{document}$2{\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^2 {\rm DMP}$\end{document}. For complete reaction, trace amounts of t-BuOMe lead to the result k2 ∼ 109 M-1 ·sec-1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - Bu}\mathop \to \limits^5$\end{document} products. From the relationship k6 = 2(k2k5a)1/2 and with k5a = 108.4 M-1 · sec-1, we arrive at the result k6 = 109.7 M-1 · sec-1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - u}\mathop {\rm B}\limits^{\rm .} \to (t{\rm - Bu)}_{\rm 2}{\rm,}t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u} + {\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^6 t{\rm - BuOMe}$\end{document}.

Notes: The kinetics of the gamma-radiation induced free-radical chain reaction in solutions of carbon tetrachloride in cyclohexane (RH) has been investigated in the temperature range of 303-383°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated cyclohexyl radicals with carbon tetrachloride. The kinetics of the following reactions were investigated: The following rate expression was obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm}k_3 /(k_4)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} ({\rm cm}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} \cdot {\rm sec}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}}) = 4.78 \pm 0.08 - (8.81 \pm 0.12)/\theta ^1$$\end{document} The error limits are the standard deviation from the least mean square Arrhenius plots. Effects of phase on the kinetics of reactions (3) and (4) are considered.

Notes: The hydrogen abstraction from asymmetrically fluorinated and chlorofluorinated ethanes by chlorine atoms has been investigated in the gas phase between 264 and 333°K using the competition method. Arrhenius parameters for the reaction on both sites of the molecules are discussed.

Notes: The life times of chemically activated alcohols have been determined using the high-pressure unimolecular rate parameters for thermal decomposition of alcohols from shocktube studies and RRKM calculations. They are compared with literature numbers (from insertion of 0(1D) into hydrocarbons). It is suggested that in some cases singlet oxygen carries excess energy into the hydrocarbon. The consequences of such an assumption are explored and discrepancies with previously published conclusions discussed.

Notes: The rate law - d[O3]/ dt = k1[A][O3] + k3[A][O3]2/ (k4 + k5[O2]) has been found to obtain for the reaction of ozone with allene and with 1,2-butadiene. We now find that this rate law also applies to the reaction of ozone with ethylene and presumably with all lower alkenes. This generalizes the inhibiting effect of oxygen and accounts for the simplifed rate law found in the presence of excess oxygen. Oxygen itself is a product of the ozone-ethylene reaction, and we find that as [O3]0 increases, the (O2 formed)/(O3 used) ratio approaches 1.5. Values of k1, k3/k5 for ethylene are compared with those for allene, 1,3-butadiene, and propene. A generalized mechanism is postulated for the reaction of ozone with alkenes involving a chain sequence that produces oxygen and which accounts for the observed rate law. A specific mechanism is postulated for the reaction of O3 with ethylene, and the thermochemistry of the chain sequence is examined in detail.

Notes: Hydrogen bromide is known to inhibit the bromination of aromatic substrates (ArH), either by fixing up bromine as HBr3 or ArH as ArH · HBr. However, there is catalysis by HBr in the bromination of mesitylene in acetic acid. The bromination of o-xylene in acetic acid in the dark is found to be autocatalytic, and the reaction is overall third order, first order in o-xylene with the orders in Br2 and HBr depending on the concentrations. A composite rate expression involving Br2 and HBr as electrophiles has been proposed and verified using iodine bromide as a catalyst where the orders are one in each of the reactants, irrespective of the concentrations used.

Notes: The reactions of O3 with CH3ONO and C2H5ONO were studied using infrared absorption spectroscopy in a static reactor at temperatures between 298 and 352K. Both reactions followed simple second-order kinetics forming the corresponding nitrate: The rate coefficients are given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_1 ({\rm cm}^{\rm 3} /{\rm molc} \cdot {\rm sec}) = (- 12.17 \pm 0.23) - (\frac{{5315 \pm 172}}{{2.303{\rm}T}})$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_2 ({\rm cm}^{\rm 3} /{\rm molc} \cdot {\rm sec}) = (- 15.50 \pm 0.16) - (\frac{{2351 \pm 116}}{{2.303{\rm}T}})$$\end{document}.

Notes: The effect of temperature on the reaction of toluene with hydrogen atoms is interpreted by the RRKM(Marcus-Rice) unimolecular rate theory. It was found that the product distribution changed markedly with temperature in the range of 300-780°K. Methyl-cyclohexadienes and methylcyclohexenes were the main products in the vicinity of room temperature, which were taken over by benzene and ethylbenzene as temperature increased. The calculation based on RRKM theory shows that the experimental results are explained in terms of the effect of temperature on the unimolecular reactions of the chemically activated methylcyclohexadienyl radicals.

Notes: The first-order rate constants for aquation of Co(NH3)5(DMF)3+ were determined in aqueous perchlorate media. The rate constants were independent of hydrogen ion concentration and ionic strength, but decreased with increasing perchlorate ion concentration. Proton magnetic resonance studies showed that dimethylformamide was not hydrolyzed to formic acid and dimethylamine in the aquation step. Mass-spectrometer studies showed that cobalt-oxygen bond breaking occurred in 98 percent, or more, of the aquation acts. Enthalpies and entropies of activation were determined. It was concluded that aquation occurred by an Id mechanism.

Notes: Metastable N2(A3Σu+), υ = 0, υ = 1, molecules are produced by a pulsed Tesla-type discharge of a dilute N2/Ar gas mixture. Rate coefficients for quenching these metastable levels by O2, O, N, and H were obtained by time-resolved emission measurements of the (0, 6) and (1, 5) Vegard-Kaplan bands. In units of cm3/mole · sec at 300°K and with an experimental uncertainty of ±20%, these rate coefficients for N2(A3Σu+) are \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm O2}} = 2.9 \times 10^{- 12}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm O}} = 1.5 \times 10^{- 11}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm N}} = 4.8 \times 10^{- 11}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm H}} = 3.5 \times 10^{- 12}$$\end{document}Within the limits of error these coefficients apply to quenching N2(A3Σu+) υ′ = 1 as well.

Notes: The BEBO method was used to calculate the kinetic isotope effect for formyl-hydrogen abstraction from acetaldehyde by methyl radicals. The calculated isotope effect and experimental ratios of the rate constants obtained at 785°K for the reactions of CH3 with CH3CHO and CH3CDO, together with the theoretical temperature dependence of the specific rates (as formulated by the BEBO theory), were used to obtain rate constants for the steps CH3 + CH3CHO → CH4 + CH3CO (2a), CH3 + CH3CHO → CH4 + CH2CHO (2b), and CH3 + CH3CDO → CH3D + CH3CO (1a) between 298 and 1224°K.It was shown that the curvature apparent in the Arrhenius plot of the rate coefficient k2 reported for the reaction of methyl radicals with acetaldehyde in the temperature range of 298-1224°K is caused both by the simultaneous contribution of steps (2a) and (2b) to methane formation, and by the curvature in the Arrhenius plots of the two elementary rate constants themselves. The predicted curve agrees well with the experimental data, especially if the tunneling correction is applied.

Notes: An absolute value of kr of ethyl radicals at 860 ± 17°K of 4.5 × 109 M-1·sec-1 was determined under VLPP conditions, where the value of kr/kr∞ should be about 1/2. Thus kr∞(M-1·sec-1) ∼ 1010 at 860°K. An error of as much as a factor of 2 in kr would be surprising, but possible.The value of 1010M-1·sec-1 seems to be a factor of from 2 to 5 too high to be compatible with extensive data on the reverse reaction and the accepted thermochemistry. Changes in the heat of formation and entropy of the ethyl radical can change the situation somewhat, but even these changes when applied to the work of Hiatt and Benson [3] indicate that ethyl combination should be ∼ 109.3 M-1·sec-1. More work is necessary if a better value is desired.

Notes: A flash photolysis system has been used to study the rate of reaction (1), OH + CH4 → CH3 + H2O, using time-resolved resonance absorption to monitor OH. The temperature was varied between 300 and 900°K. It is found that the Arrhenius plot of k1 is strongly curved and k1 (T) can best be represented by the expression \documentclass{article}\pagestyle{empty}\begin{document}$$k = 10^{3.54 \pm 0.08} T^{3.08} \exp (- 1010/T){\rm cm}^{\rm 3} /{\rm mole} \cdot {\rm sec}{\rm .}$$\end{document}The apparent Arrhenius activation energy changes from 15±1 kJ/mole at 300°K to 32±2 kJ/mole at 1000°K. On either side of our temperature range, both absolute rates and their temperature dependence are in good agreement with the results from most previous investigations.

Notes: The Diels-Alder addition of acrolein to cyclohexa-1,3-diene has been studied between 486 and 571°K at pressures ranging from 55 to 240 torr. The products are endo- and exo-5-formylbicyclo[2.2.2]oct-2-ene (endo- and exo-FBO), and their formations are second order. The rate constants (in l./mole · sec) are given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_{{\rm endo}} = -(19,470 \pm 50)/4.576T + (5.65 \pm 0.02)$$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_{{\rm exo}} = - (20,630 \pm 50)/4.576T + (5.51 \pm 0.02)$$\end{document}The retro-Diels-Alder pyrolysis of endo-FBO has also been studied. In the ranges of 565-638°K and 6-38 torr, the reaction is first order, and its rate constant (in sec-1) is given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_{{\rm p}} = - (46,390 \pm 110)/4.576T + (12.98 \pm 0.04)$$\end{document}The reaction mechanism is discussed. The heat of formation and the entropy of endo-FBO are estimated.

Notes: Absolute rate constants for the reaction of O(3P) atoms with CH2 = CHF, CH2 = CHCl, and CH2 = CHBr have been obtained at 298 ± 2°K using a modulation phase shift technique. The rate constants (k2 × 10-8 l./mole · sec) obtained are: CH2 = CHF (1.61 ± 0.20), CH2 = CHCl (2.54 ± 0.26), and CH2 = CHBr (2.45 ± 0.25). These rate constants are lower than those determined by discharge flow techniques, but that for CH2 = CHF is in good agreement with relative rate measurements.

Notes: The recombination of chlorine atoms has been investigated by flash photolysis in the inert gases He, Ne, Ar, N2, CO2, CF4, SiF4, SF6, and C2F6. The pressure dependence of the reaction has been measured between 0.5 and about 100 atm for He, N2, and CO2. Experiments on the NO-catalyzed recombination of chlorine in the presence of He (0.5-100 atm) permitted a determination of the falloff curve of the reaction Cl+NO(+He)→ClNO(+He).

Notes: Nanosecond flash photolysis of b-nitronaphthalene (b-NO2C10H7) in nonpolar and polar solvents shows a transient species with maximum absorption and lifetime dependent on solvent polarity. In deaerated n-hexane the absorption maximum and lifetime (1/k) are 425 nm and 530 nsec, while in deaerated ethanol the corresponding values are 470 nm and 1.7 ·sec. This transient absorption is attributed to the triplet excited state of b-NO2C10H7, and the observed red shift as well as its longer lifetime in polar solvents are indicative of the intramolecular charge transfer character of this state. The change of dipole moment accompanying the transition T1 → Tn, as well as rate constants for electron and proton transfer reactions involving the T1 state of b-NO2C10H7, were determined. The spectroscopic and kinetic data obtained in this work indicate that the triplet state of b-NO2C10H7 behaves like a n-π* state in nonpolar media, while in polar solvents the n-π* character of the state is reduced with a simultaneous increase in the charge transfer character.

Notes: The thermal isomerization of 1-chloro-4-methylbicyclo[2.2.0]hexane and 1-chloro-4-lthylbicyclo[2.2.0]hexane has been studied in the gas phase and in tetrachloroethylene and o-dichlorobenzene solvents over the temperature range of 409-512°K. Good first-order kinetics yield the following Arrhenius equations: log kg/(sec-1) = (13.86 ± 0.03) - (36.90 ± 0.07)/middot; log ka/(sec-1) = (13.55 ± 0.31) - (35.50 ± 0.13)/θ log kb/(sec-1) = (13.55 ± 0.15) - (35.87 ± 0.06)/θ for the 4-methyl derivative, and log ka/(sec-1) = (13.68 ± 0.29) - (36.19 ± 0.13)/· log kb/(sec-1) = (13.55 ± 0.15) - (35.87 ± 0.06)/θ for the 4-ethyl derivative. The subscripts g, a, and b refer to the gas phase, tetrachloroethylene, and o-dichlorobenzene as solvents, respectively, θ = 2.303 RT kcal/mole, and the error limits are least squares deviations. The activation energy is increased by 1.2 ± 0.5 kcal/mole for a methyl group and 1.5 ± 0.5 kcal/mole for an ethyl group with respect to the unsubstituted bridgehead compound. With reference to the reported Arrhenius parameters for all bicyclo[2.2.0]hexane isomerizations, it is shown that this increase in activation energy with alkyl substitution is not due to the steric interaction in the transition complex. It is postulated that the ground-state reactant bicyclo[2.2.0]hexane molecules are stabilized by alkyl substitution. This ground-state alkyl stabilization of small ring compounds may also account for an increase in the activation energy on pyrolysis of alkyl substituted cyclopropanes and cyclobutanes.

Notes: The kinetics of the gamma-radiation induced free-radical chain reaction in solutions of carbon tetrachloride in n-hexane (RH) was investigated in the temperature range of 297.5-373°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated hexyl radicals with carbon tetrachloride. The kinetics of the following reactions were investigated: The following rate expression was obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_3 /k_4 ^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} ({\rm cm}^{{\raise0.7ex\hbox{${\rm 1}$} \!\mathord{\left/ {\vphantom {{\rm 1} {\rm 2}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\rm 2}$}}} /{\rm mole}^{{\raise0.7ex\hbox{${\rm 1}$} \!\mathord{\left/ {\vphantom {{\rm 1} {\rm 2}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\rm 2}$}}} \cdot {\rm sec}^{{\raise0.7ex\hbox{${\rm 1}$} \!\mathord{\left/ {\vphantom {{\rm 1} {\rm 2}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\rm 2}$}}}) = 5.19 \pm 0.05 - (9.62 \pm 0.10)\theta $$\end{document}where θ = 2.303 RT in kcal/mole. The error limits are the standard deviation from the least mean square Arrhenius plots. It is concluded that reaction (4) is diffusion controlled in the liquid phase, and that the activation energies in the gas and liquid phases of reaction (3) are equal.

Notes: An approximate method of analyzing nonlinear reaction models in modulated molecular beam surface kinetic studies is developed. The exact method for treating nonlinear surface mechanisms is tedious and almost always requires computer analysis. The proposed approximate method is a simple extension of the Fourier expansion technique valid for linear surface reactions; it quickly provides analytical expressions for the phase lag and amplitude of the reaction product for any type of nonlinear surface mechanism, which greatly facilitates comparison of theory and experiment. The approximate and exact methods are compared for a number of prototypical adsorption-desorption reactions which include coverage-dependent adsorption and desorption kinetics of order greater than unity. Except for certain extreme forms of coverage-dependent adsorption, the approximate method provides a good representation of the exact solution. The errors increase as the nonlinearities become stronger. Fortunately, when the discrepancy between the two methods is substantial, the reaction product signal is so highly demodulated that reliable experimental data usually cannot be obtained in these regions anyway.

Notes: Atomic absorption and fluorescence spectrophotometry have been routinely used in kinetic investigations as probes of relative, rather than absolute, atom concentration. The calibration of a Lyman-α photometer for measurement of absolute hydrogen atom concentrations at levels [H] ι ≤ 1.8 × 1014 atoms/cm2 and total pressure of 1.5 torr He is described. The photometer is characterized in terms of a two-level emission source and an absorption region in which only Doppler broadening of the transition is considered. The modifications due to pressure broadening by high pressures (500 ≤ P ≤ 1500 torr) in the absorption region are discussed in detail. Application of the technique is reported for the recombination of hydrogen atoms in the presence of six nonreactive heat bath gases. Experiments were performed in a static reaction cell at pressures of 500-1500 torr of heat bath gas, and hydrogen atoms were produced by Hg (3P1) photosensitization of H2. The technique is critically evaluated and the mechanistic implications of the hydrogen atom recombination results are examined. The measured room temperature recombination rate constants in H2, He, Ne, Ar, Kr, and N2 are 8.5 ± 1.2, 6.9 ± 1.5, 5.9 ± 1.5, 8.0 ± 0.8, 10.2 ± 0.9, and 9.6 ± 1.4, respectively, where the units are 1033 cm6/molec2 · sec.

Notes: The gamma radiation induced decomposition of MeSO2Cl in cyclohexane (RH) was studied between 60 and 150°C. Throughout this temperature range the reaction proceeds by a free radical chain mechanism. Its propagation is described by the following reactions: The kinetic analysis of the results of the experiments with added SO2, which were carried out in the temperature range of 80 to 150°C, gives 14.94 ± 0.92 and 11.91 ± 0.82 kcal/mole for D(Me-SO2) and D(c-C6H11-SO2), respectively. These bond dissociation energies are considerably lower than the gas-phase values, and the possible cause of this difference is discussed. Present results also seem to indicate that D(MeSO2-H) does not exceed 95 kcal/mole. Competitive experiments with added tetrachloroethylene result in \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_{2{\rm a}} (1./{\rm mole} \cdot {\rm sec}) = 9.07 \pm 0.17- (4.92 \pm 0.21)/\theta $$\end{document} where θ = 2.303RT in kcal/mole.

Notes: Several fluorine-containing ethanes (monofluoro, 1,1-difluoro, 1,1,1-trifluoro, 1,1,2-trifluoro, 1,1,2,2-tetrafluoro, and pentafluoro) and ethenes (1,1-difluoro and trifluoro) form hydrogen fluoride when irradiated with gamma rays in the gas phase at 25°C. Hydrogen fluoride is apparently formed from fluoroethanes by a mechanism which involves formation of an intermediate semiion pair. We observed identical HF yields both in the absence and presence of molecular oxygen, except for monofluoroethane. A reduction of G(HF) with increasing sample pressure, for example, of 1,1,2,2-tetrafluoroethane, indicates that collisional stabilization of excited fluoroethane molecules competes with the process of HF elimination. High G values for HF and CO2 in mixtures of CF2=CFH and O2 reveal the occurrence of a chain reaction.

Notes: The reaction of methyl radicals with atomic and molecular oxygen was studied with a photoionization mass spectrometer. The methyl radicals were generated by reacting oxygen atoms with ethylene in a fast-flow tube reactor. The rate constant for the reaction of methyl radicals with oxygen atoms was (1.0 ± 0.2) × 10-10 cm3/molec · sec with no significant variation with temperature over the range of 259-341°K. The reaction of methyl radicals with molecular oxygen involves both a two-body reaction, having a rate constant \documentclass{article}\pagestyle{empty}\begin{document}$\begin{array}{*{20}c} {k_{{\rm 3a}} = (10^{- 12.54 \pm 0.35})\exp [(- 940 \pm 250)T^{- 1}]} & {{\rm cm}^{\rm 3} /{\rm molec} \cdot {\rm sec}} \end{array}$\end{document} and a three-body recombination having a negative temperature dependence. The methyl peroxy radical could be observed at its steady-state concentration. The rate constants determined at low pressures are compatible with the values determined at higher pressures by flash photolysis. Formaldehyde appears to be a major product of the two-body reaction of CH3 with O2, and also of the reaction of CH3O2 with oxygen atoms.

Notes: The kinetics of gas-phase reaction of CH3CF2I with HI were studied from 496 to 549K and have been shown to be consistent with the following mechanism: A least squares treatment of the data gave \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_1 (M^{- 1} \cdot \sec ^{- 1}) = (11.4 \pm 0.3) - \frac{{(15.7 \pm 0.8)}}{\theta}$$\end{document} where θ = 2.303 RT kcal/mole. The observed activation energy E1 was combined with E2 = 0 ± 1 kcal/mole to yield \documentclass{article}\pagestyle{empty}\begin{document}$$DH^ \circ ({\rm CH}_{\rm 3} {\rm CF}_2 - {\rm I}) = 52.1 \pm 1.0{\rm kcal}/{\rm mole}$$\end{document} The result, combined with data for several C—I bond dissociation energies, leads us to conclude that the C(sp3)—I bond is relatively insensitive to F for H substitution and that the C(sp2)-I bond has considerable double-bond character.

Notes: Photolysis of the vapour of hexafluoroacetylacetone HFAA in its enolic form involves decomposition by two independent primary processes, one of which is a novel elimination of HF giving 2,2-difluoro-2,3-dihydro-5-trifluoromethylfuran-3-one: The HF is not vibrationally excited. Photolysis of the cyclic product of reaction (5) yields CF2 radicals which, if HFAA is present, undergo an insertion into the enolic OH bond, (9)The infrared, ultraviolet, nuclear magnetic resonance, and mass spectra of HFAA and of the products of reactions (5) and (6) have been measured. Approximate quantum yields for reactions (1) and (5) have been obtained. Both φ1 and φ5 depend on pressure and the ratio φ1/φ5 increases with temperature and decreased wavelength of photolysing light. It is proposed that the ratio φ1/φ5 increases as the vibrational energy of electronically excited HFAA increases.

Notes: The decomposition of ethane sensitized by isopropyl radicals was studied in the temperature range of 496-548°K. The rate of formation of n-butane, isopentane, and 2,3-dimethylbutane were measured. The expression k1/k2½ was found to be \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm}k_1 /k_2 ^{1/2} ({\rm dm}^{{\rm 3/2}} /{\rm mol}^{{\rm 1/2}} \cdot \sec ^{1/2}) = (3.2 \pm 0.4) - (54 \pm 3{\rm kJ/mol})/2.3RT$$\end{document} where k1 and k2 are rate constants of The decomposition of propylene sensitized by isopropyl radicals was studied between 494 and 580°K by determination of the initial rates of formation of the main products. The ratio of k13/k21/2 was evaluated to be \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm}k_{13} /k_2 ^{1/2} ({\rm dm}^{{\rm 3/2}} /{\rm mol}^{{\rm 1/2}} \cdot \sec ^{1/2}) = (1.9 \pm 0.7) - (32 \pm 7{\rm kJ/mol})/2.3RT$$\end{document} where k13 is the rate constant for The isomerization of the isopropyl radical was investigated by studying the decomposition of azoisopropane. The decomposition of the iso-C3H7 radical into C2H4 and CH3 was followed by measuring the rate of formation of C2H4. On the basis of the experimental data, obtained in the range of 538-666° K, k15/k2½ was found: \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm}k_{15} /k_2 ^{1/2} ({\rm mol}^{{\rm 1/2}} /{\rm dm}^{{\rm 3/2}} \cdot \sec ^{1/2}) = (9.3 \pm 0.8) - (152 \pm 9{\rm kJ/mol})/2.3RT$$\end{document} where k15 is the rate constant of

Notes: The photolysis of SO2 at 3080 Å, FWHM = 150 Å, and 22°C has been investigated in the presence of cis- and trans-C2F2H2. Quantum yield measurements for the photosensitized isomerization of cis-C2F2H2 to trans-C2F2H2 have been made for a variation in the [SO2]/[cis-C2F2H2] ratio from 0.992 to 253. The results fit a mechanism which is consistent with the SO2(3B1) state being the reactive excited state of sulfur dioxide. A mechanism employing only the SO2(1B1) and SO2(3B1) excited states is quite satisfactory to rationalize the data. A value for the SO2 collisionally induced intersystem crossing efficiency from SO2(1B1) to SO2(3B1) of 0.35 ± 0.14 was estimated while the cis-C2F2H2 efficiency was found to be 0.030 ± 0.012. The rate constant at 22°C for the removal of SO2(3B1) molecules by cis-C2F2H2 was found to be (1.43 ± 0.13) × 10101./mole · sec. A photostationary composition, [cis]/[trans] = 1.0 ± 0.1, was found from prolonged irradiations of SO2 in the presence of the cis and trans isomers.

Notes: Aquation rates forcis-CoCl(en)2(A)2+ (A = 3,5-lutidine, imidazole, N-methylimidazole, benzimidazole) have been determined by halide release titration in 1.0 M HNO3 at 50-80°C. Kinetic parameters are (in the above order of A) 107k298 (sec-1), 7.4, 5.7, 1.3, 9.7; Ea (kJ/mole), 103, 101, 130, 112; log PZ (sec-1), 11.89, 11.53, 16.04, 13.58; ΔS298

Notes: Crossed molecular beam techniques have been used to study the endoergic reaction between F2 and I2. Above a threshold energy of 4 kcal/mole the observed products are I2F and F. At higher energies IF is also produced. Angular and velocity distributions indicate that the IF does not result from a four-center exchange reaction.

Notes: Rate constants and activation parameters are reported for the decarboxylation of methylmalonic acid and n-octadecylmalonic acid in three normal alkanols (hexanol-1, octanol-1, and decanol-1). Enthalpies of activation for both substrates in the various solvents are found to be a linear function of the number of carbon atoms or methylene groups in the hydrocarbon chain of the solvent. For both reaction series the isokinetic temperature is found to be equal to the melting point of the substrate. The free energy of activation at the isokinetic temperature in kcal/mole is 29.0 for n-octadecylmalonic acid and 29.4 for methylmalonic acid. Based on the results of the present investigation as well as on previously reported data in the case of malonic acid and n-butylmalonic acid, an empirical method of calculating the rate of reaction for the decarboxylation of malonic acid and its n-alkyl derivatives in normal alkanols is proposed. As a further test of the method of calculation the decarboxylation of n-dodecylmalonic acid in heptanol-1 at 110.30°C was studied. The calculated value of the pseudo-first-order specific reaction velocity constant of the reaction agreed with the experimental value to within about 0.1 percent.

Notes: The kinetics of chlorine atom abstraction from the chloromethanes (ClM), CCl4, CHCl3, CH2Cl2, and CH3Cl by radiolytically generated trichlorosilyl radicals was studied in the liquid phase by a competitive method. Arrhenius parameters of chlorine atom abstraction from chloromethanes relative to that of bromine atom abstraction from cyclohexyl bromide (RBr) were as follows: The error limits are two standard deviations (2σ) from least mean square Arrhenius plots. From the linear correlation between Ecl values derived from the reactions of SiCl3 and cyclohexyl radicals with the ClM series it is estimated that Ecl (R + CH3Cl) ≃ 16 kcal/mole. In addition the relative Arrhenius parameters for the hydrogen atom abstraction from SiHCl3 and chlorine atom abstraction from CCl4 by cyclohexyl radicals were obtained log AH/Acl = 0.12 ± 0.15 and EH - Ecl = 0.24 ± 0.26. The EH - Ecl value was combined with existing data on E(R + CCl4) to yield the EH(R + SiHCl3) value.

Notes: The isomerization of cycloheptatriene at high temperatures (800-1250°K) has been studied experimentally using a shock tube at high pressures and by very low-pressure pyrolysis in the intermediate-pressure region (the first direct use of the latter technique for an isomerization). Rate coefficients obtained are in accord with previous results at lower temperatures. The results are examined theoretically to account for weak-collision nonequilibrium effects. These corrections are found to be appreciable at the temperatures studied.

Notes: Rate constants of change transfer reactions kCT, involving C3—C9 alkanes and cycloalkanes, have been determined in an ion cyclotron resonance mass spectrometer. The rate constants are significantly lower than the corresponding rate constants for collision when the reaction is less than about 0.5 eV exothermic for linear alkane ions, or less than about 0.2 eV exothermic for cycloalkane ions. In this region of low reaction efficiency, the efficiency of reaction with linear or branched alkanes seems to depend primarily on reaction exothermicity. (The efficiencies of reaction of a given ion with cyclic alkanes also depend on ΔHrn, but are higher than for reactions with other compounds). Although the lowered reaction efficiencies probably result, at least in part, from unfavorable Franck-Condon factors in the energy range near the ionization onset, quantitative correlations between reaction efficiency and estimated relative Franck-Condon factors were not observed. When the enthalpy of reaction is small (less than about -0.15 eV), it is seen that the reverse charge transfer can also occur, and equilibrium is established under the conditions of these experiments. From the observed equilibrium constants, values for the standard free energy change are derived, and assuming that ΔS is small for electron transfer equilibria, values of ΔHrn are estimated. In the case of the equilibria involving cyclohexane ion, these values of ΔHrn lead to estimates of the ionization potentials of methylcyclopentane, 3-methylpentane, n-octane, 2,2-dimethylbutane, and 2,3-dimethylbutane, which are lower than the ionization potentials of cyclohexane, that is, 〈9.88 eV, although all these compounds had previously been reported to have ionization potentials above 10.03 eV. That the ionization potentials are indeed lower than 10.03 eV is confirmed by determining the quantum yields of ionization with 10.03-eV photons.It is pointed out that the conclusions reached here apparently also apply to the charge transfer reactions of alkane ions in the liquid phase.

Notes: The application of the RRKM theory to the reverse bimolecular reaction of the amine-borontrifluoride system has been made. The results are in good agreement with experiments.

Notes: New experimental data have been obtained for H + C2H2, D + C2H2, H + C2D2, and D + C2D2 at room temperature. Two previously described apparatus were used in order to measure the pressure dependence of the reactions. The absolute rate constants are compared to results from other laboratories. The present results and those of Payne and Stief are used to obtain the high-pressure limiting rate constant at room temperature. When the activation energy from the work of Payne and Stief is considered, it is shown that the A factor for H + C2H2 is too low by a factor of ∼20. If a transmission coefficient is introduced which is constant for all isotopic variations, the pressure dependence can be explained in terms of the randomly energized radicals. RRKM theory is then invoked to explain the observed statistical nonequilibrium kinetic isotope effects.

Notes: Tandem chemical laser techniques have been used to detect HF formed through photoelimination from 1,1,1,5,5,5-hexafluoroacetylacetone, HFAA. Information about the HF vibrational population ratios is deduced: N2/N1 〈 0.37 and N1/N0 〈 0.45. This work supports the deduction by Bassett and Whittle that photodecomposition of the enol form of HFAA results mainly in HF elimination and ring closure to a dihydrofuranone, a new type of reaction.

Notes: The photolysis of SO2 in the presence of cis- and trans-2-pentene has been investigated at 3660 Å and 22°C. Quantum yield measurements of the SO2 photosensitized conversion of one isomer into the other are consistent with a mechanism in which the only participating excited electronic state of SO2 is the SO2(3B1) state. Quantum yield measurements were made for a variation in PSO2/Pisomer reactant ratios of 4.01-283 and 57.5-351 for the cis and trans isomers, respectively. The data are consistent with a mechanism in which a (SO2-olefin)3 collision intermediate is the precursor to the photosensitized isomeric products. The intermediate undergoes unimolecular decay to yield the cis and trans isomers with probabilities of 0.26 ± 0.05 and 0.69 ± 0.04, respectively. Estimates of the quenching rate constants at 22°C for removal of SO2(3B1) molecules by cis- and trans-2-pentene are (0.633 ± 0.125) × 1011 l./mole/sec and (1.00 ± 0.27) × 1011 l./mole/sec, respectively. An experimentally determined photostationary composition, [trans-2-pentene]/[cis-2-pentene] = 2.3 ± 0.1 was in fair agreement with that of 1.7 ± 0.7 as predicted from kinetic data derived in this study.

Notes: The rate of decomposition of s-butyl nitrite (SBN) has been studied in the absence (130-160°C) and presence (160-200°C) of NO. Under the former conditions, for low concentrations of SBN (6 × 10-5 - 10-4M) and small extents of reaction (∼1.5%), the first-order homogeneous rates of acetaldehyde (AcH) formation are a direct measure of reaction (1) since k3c » k2(NO): . Unlike t-butyl nitrite (TBN), d(AcH)/dt is independent of added CF4 (∼0.9 atm). Thus k3c is always » k2 (NO) over this pressure range. Large amounts of NO (∼0.9 atm) (130-160°C) completely suppress AcH formation. k1 = 1016.2-40.9/θ sec-1. Since (E1 + RT) and ΔH°1 are identical, within experimental error, both may be equated with D(s-BuO-NO) = 41.5 ± 0.8 kcal/mol and E2 = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result ΔH°f (s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document}) = - 16.6 ± 0.8 kcal/mol. From ΔS°1 and A1, k2 is calculated to be 1010.4 M-1 · sec-1, identical to that for TBN. From an independent observation that k6/k2 = 0.26 ± 0.01 independent of temperature, \documentclass{article}\pagestyle{empty}\begin{document}${\rm s - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}, we find E6 = 0 ± 1 kcal/mol and k6 = 109.8M-1 · sec-1. Under the conditions first cited, methyl ethyl ketone (MEK) is also a product of the reaction, the rate of which becomes measurable at extents of conversion 〉2%. However, this rate is ∼0.1 that of AcH formation. Although MEK formation is affected by the ratio S/V for different reaction vessels, in a spherical reaction vessel, this MEK arises as the result of an essentially homogeneous first-order 4-centre elimination of HNO. \documentclass{article}\pagestyle{empty}\begin{document}${\rm SBN}\mathop \to \limits^{\rm 5} {\rm MEK} + {\rm HNO}$\end{document}; k5 = 1012.8-35.8/θ sec-1. Sec-butyl alcohol (SBA), formed at a rate comparable to MEK, is thought to arise via the hydrolysis of SBN, the water being formed from HNO. The rate of disappearance of SBN, that is, d(MEK + SBA + AcH)/dt, is given by kglobal = 1015.7-39.6/θ sec-1. In NO (∼1 atm) the rate of formation of MEK was about twice that in the absence of NO, whereas the SBA was greatly reduced. This reaction was also affected by the ratio S/V of different reaction vessels. It was again concluded that in a spherical reaction vessel, the rate of MEK formation was essentially homogeneous and first order. This rate is given by kobs = 1012.9-35.4/θ sec-1, very similar to k5. However, although it is clear that the rate of formation of MEK is doubled in the presence of NO, the value for kobs makes it difficult to associate this extra MEK with the disproportionation of s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document} and NO: s-\documentclass{article}\pagestyle{empty}\begin{document}$s{\rm - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}. NO at temperatures of 130-160°C completely suppresses AcH formation. AcH reappears at higher temperatures (165-200°C), enabling k3c to be determined. Ignoring reaction (6), d(AcH)/dt = k1k3 (SBN)/[k3c + k2(NO)]; k3c = 1014.8-15.3/θ sec-1. Inclusion of reaction (6) into the mechanism makes very little difference to the result. Reaction (3c) is expected to be a pressure-dependent process.

Notes: Mixtures of N2O, CO, and NO in excess H2 were photolyzed at 213.9 nm and 298°K. The initially formed O(1D) atoms from the photolysis of N2O abstract an H atom from H2 permitting a study of the competition: From the CO2 yield the relative rate coefficient k1/k2 is obtained. It is found to be slightly dependent on pressure for total pressures (mainly H2) of 95.5 to 768 torr. However, the values are near the high-pressure limiting value which is found by extrapolation to give k1∞ = 1.2 × 10-11 cm3/sec based on k2∞ = 3.55 × 10-13 cm3/sec.

Notes: The rate of decomposition of t-butyl nitrite (TBN) has been studied in a static system over the temperature range of 120-160°C. For low concentrations of TBN (10-5- 10-4M), but with a high total pressure of CF4 (∼0.9 atm) and small extents of reaction (∼1%), the first-order homogeneous rates of acetone (M2K) formation are a direct measure of reaction (1), since k3» k2 (NO): TBN . Addition of large amounts of NO in place of CF4 almost completely suppresses M2K formation. This shows that reaction (1) is the only route for this product. The rate of reaction (1) is given by k1 = 1016.3-40.3/θ s-1. Since (E1 + RT) and ΔH°1 are identical, both may be equated with D(RO-NO) = 40.9 ± 0.8 kcal/mole and E2 = O ± 1 kcal/mole. From ΔS°1 and A1, k2 is calculated to be 1010.4M-1 ·s-1, implying that combination of t—BuO and NO occurs once every ten collisions. From an independent observation that k2/k2′ = 1.7 ± 0.25 independent of temperature, it is concluded that k2′ = 1010.2M-1 · s-1 and k1′ = 1015.9-40.2/θ s-1; . This study shows that MeNO arises solely as a result of the combination of Me and NO. Since NO is such an excellent radical trap for t-Bu\documentclass{article}\pagestyle{empty}\begin{document}${\rm Me\dot O}$\end{document}, reaction (2) may be used in a competitive study of the decomposition of t—Bu\documentclass{article}\pagestyle{empty}\begin{document}${\rm Me\dot O}$\end{document} in order to obtain the first absolute value for k3. Preliminary results show that k3 (∞) = 1015.7-17.0/θ s-1. The pressure dependence of k3 is demonstrated over the range of 10-2-1 atm (160°C). The thermochemistry for reaction (3) implies that the Hg 6(3P1) sensitised decomposition of t-BuOH occurs via reaction (m): In addition to the products accounted for by the TBN radical split, isobutene is formed as a result of the 6-centre elimination of HONO: TBN \documentclass{article}\pagestyle{empty}\begin{document}$\mathop \to \limits^7 $\end{document} isobutene + HONO. The rate of formation of isobutene is given by k7 = 1012.9-33.6/θ s-1. t-BuOH, formed at a rate comparable to that of isobutene-at least in the initial stages-is thought to arise as a result of secondary reactions between TBN and HONO. The apparent discrepancy between this and previous studies is reconciled in terms of the above parallel reactions (1) and (7), such that k + 2k7 = 1014.7-36.2/θ s-1.

Notes: The kinetics of the oxidation of iodide by hydrogen peroxide catalyzed by acidic molybdate have been studied by a spectrophotometric stopped-flow method. The results are interpreted in terms of the mechanism and the implied rate law \documentclass{article}\pagestyle{empty}\begin{document}$$ - d[{\rm H}_{\rm 2} {\rm O}]/dt = \frac{{k_4 k_1 k_2 [{\rm H}_2 {\rm O}_2]^2 [{\rm mol}][{\rm I}^ -]}}{{1 + k_1 [{\rm H}_2 {\rm O}_2] + k_1 k_2 [{\rm H}_2 {\rm O}_2]^2 + {\rm K}_{\rm 3} [{\rm I}^{\rm -}]}}$$\end{document}where [mol] is total analytical concentration of molybdate. The values obtained for the rate and equilibrium constants are k4 = (3.3 ± 1) × 102 1./mole · s, K1 = (1.2 ± 0.6) × 104 1./mole, K2 = (1.3 ± 0.7) × 103 1./mole, and K3 = (4 ± 3) × 102 1./mole at 298°K.

Notes: The chemical activation data for three- and four-centered hydrogen fluoride elimination from CH2FCDF2 have been analyzed to assign the energy released to the olefin fragment in the three-centered process and to estimate the threshold energies for elimination channels. Based upon the cis-trans isomerization rates of CHF = CHF, 78% of the total available energy was released to the olefin fragment for the αα channel. The analysis suggests the existence of an appreciable barrier (∼10 kcal/mole) for the reverse reaction, addition of the CH2FCF carbene to DF. The threshold energies for αα, αβ, and βα elimination from 1,1,2-trifluoroethane-1-d1 were assigned as 71, 68, and 68 kcal/mole, respectively. Analysis of the chemical activation data for 1,1,2,2,-tetrafluoroethane, without distinguishing between the three- and four-centered elimination channels, suggests a threshold energy of ∼75 kcal/mole.

Notes: An analytical and kinetic study of the thermal reaction of cis- or trans-2-butene has been performed in a static system over the temperature range of 480-550°C and at a low extent of reaction and initial pressures of 10-100 torr.The rate constant of the unimolecular cis-trans isomerization of cis-2-butene, determined under the conditions\documentclass{article}\pagestyle{empty}\begin{document}$$k_{ct} = 10^{13.6 \pm 0.3 - 62,000 \pm 1000/2.3{\rm RT}} {\rm sec}^{- 1} $$\end{document}(2.3 RT in cal/mole) is in good agreement with previous measurements made at lower pressures.A comparison between the formation rates of hydrogen from the thermal reactions of cis- and trans-2 butene around 500°C leads to the rate constant value\documentclass{article}\pagestyle{empty}\begin{document}$$k_m = 10^{13 \pm 0.5 - 65,500 \pm 2000/2.3{\rm RT}} {\rm sec}^{- 1} $$\end{document}(2.3 RT in cal/mole) for the unimolecular 1,4—hydrogen elimination from cis—2—butene.

Notes: The reaction of O(1D) with CH4 was studied to determine the efficiency of H2 production in a direct process, and it was found to be 0.11 ± 0.02. Thus the two channels which account for all of the reaction between O(1D) and CH4 in the gas phase are

Notes: Hydroxyl radicals were prepared from the photolysis of N2O at 213.9 nm in the presence of excess H2. The O(1D) produced in the primary photolytic act reacts with H2 to produce OH radicals. If CO is also present, then OH can react either with H2 or CO: The competition between reactions (1) and (2) was measured by measuring the CO2 yield at various values of the ratio [CO]/[H2] at 217-298°K. At 298°K the ratio of the rate coefficients k1/k2 increased with pressure from a low-pressure limiting value of 14 to a high-pressure limiting value of 50. The low-pressure limiting value agrees well with the low-pressure values found by others. At lower temperatures our high-pressure values of k1/k2 were larger than deduced from the accepted low-pressure Arrhenius expression and could be fitted to the expression \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 ^\infty /k_2 = 0.20{\rm exp (} + 3400/RT{\rm)}$$\end{document}The mechanism which seems to fit the results best is with k1° = kakb/k-a and k1∞ = ka.

Notes: The Co(NH3)5OH23+ ion reacts with malonate to form Co(NH3)5O2CCH2CO2H2+ or Co(NH3)5O2CCH2CO2+, depending on the pH of the reaction solution. The kinetics of this anation reaction have been studied as a function of [H+] for the acidity range 1.5 ≤ pH ≤ 6.0 in the temperature range of 60 to 80°C, the [total malonate] ≤ 0.5 M, and the ionic strength 1.0M. The anation by malonic acid follows second-order kinetics, the rate constant being 8.0 × 10-5 M-1·sec-1 at 70°C, and the anations by bimalonate (Q1, k1) and malonate ion (Q2, k2) are consistent with an Id mechanism. Typical values at 70°C for the ion pair formation constants are Q1 = 1.3, Q2 = 5.4M-1; and for the interchange rate constants k1 = 5.3 × 10-4; k2 = 7.3 × 10-4 sec-1. The activation parameters for the various rate constants are reported and the results discussed with reference to previously reported data for similar systems.

Notes: Direct determinations of the rate constants (cm3/molec · sec) k1, k2, and k3 from 298 to 299°K are reported, using atomic resonance fluorescence in discharge flow systems: One standard deviation.The rate constant k1, which has not been determined previously, was found to possess an insignificant temperature coefficient (EA = (0 ± 700) J/mole) in the range of 299 to 619°K.The present result for k2 agrees well with reinterpreted values from the one previous determination. Measurements of O atom consumption rates and Br atom production rates in the O + Br2 reaction are interpreted to give an estimate of the rate constant k4, which has not been reported previously, at 298°K: k3 has been measured at three temperatures between 299 and 602°K. The present and previous results for k3 were combined to give the following rate expression: \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_3 = (- 11.38 \pm 0.19) - (594 \pm 58)/T$$\end{document}

Notes: In order to describe the kinematical behavior of the bimolecular chmical reaction in a dilute solution of species characterized by a single diffusion coefficient and by some nonuniform spatial distribution of the active site, a diffusion equation with a simple sink term is derived by reducing the many-body problem to a one-body problem. The equation is normalized with the concentration of unreacted particles. The so-called second-order reaction rate constant can be calculated from the solution of the equation. The equation is applied to the intermolecular termination reaction of polymer radicals on the assumption of free draining. The reaction rate constant gradually decreases with time.

Notes: Quantum yield measurements for the SO2(3B1) photosensitized isomerization of cis-1,2-difluoroethylene have been made at 3712 Å and 22°C. The [SO2]/[cis-C2F2H2] ratio was varied from 47.4 to 455 and the quantum yield measurements over this variation of concentration ratios were consistent with a mechanism in which SO2(3B1) molecules and the cis isomer form a collision intermediate which decomposes with a probability of 0.42 ± 0.17 and 0.58 ± 0.17 of producing trans- and cis-1,2-difluoroethylene, respectively. When SO2 was subjected to prolonged irradiations in the presence of initially either pure cis- or pure trans-1,2-difluoroethylene, a photostationary composition, [cis]/[trans] = 1.0 ± 0.2, was obtained. The rate constant at 22°C for removal of SO2(3B1) molecules by cis-1,2-difluoroethylene was estimated to be (1.72 ± 0.72) × 1010 1./mole · sec.

Notes: Nanosecond flash photolysis of 1,4-dinitronaphthalene (1,4-DNO2N) in aerated and deaerated solvents shows a transient species with absorption maximum at 545 nm. The maximum of the transient absorption is independent of solvent polarity and its lifetime seems to be a function of the hydrogen donor efficiency of the solvent. The transient absorption is attributed to the lowest excited triplet state of 1,4-DNO2N. The reactivity of this state for hydrogen abstraction from tributyl tin hydride (Bu3SnH), Kq = 3.8 × 108M-1 sec, is almost equal to that of nitrobezene triplet state which has been characterized as an n → π* state. Based on spectroscopic and kinetic evidence obtained in the present work, the triplet state of 1,4-DNO2N behaves as an n → π* state in nonpolar solvents, while in polar solvents the state is predominantly n → π* with a small amount of intramolecular charge transfer character.

Notes: Concentration-time profiles have been measured for hydroxyl radicals generated by the shock-tube decomposition of hydrogen peroxide in the presence of a variety of additives. At temperatures close to 1300°K the rate constants for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm OH} + {\rm RH} \to {\rm R} + {\rm H}_{\rm 2} {\rm O}$$\end{document} are found to be in the ratio 0.18:0.19:0.59:1.00:2.33:2.88 for the additives CO:CF3H:H2:CH4:C2H4:C2H6, respectively.

Notes: The photolysis of SO2 at 3712 Å in the presence of the 1,2-dichloroethylenes has been investigated at 22deg;C. The data are consistent with the SO2(3B1) photosensitized isomerization of the 1,2-dichloroethylene isomer. A kinetic treatment of the initial quantum yield data was consistent with the formation of a polarized charge-transfer intermediate whenever SO2(3B1) molecules and one of the 1,2-dichloroethylene isomers collide which ultimately decays unimolecularly to the cis-isomer with a probability of 0.70 ± 0.26 and to the trans-isomer with a 0.37 ± 0.16 probability. Quenching rate constants for removal of SO2(3B1) molecules by cis- and trans-1,2-dichloroethylene have been estimated from quantum yield data and from laser excited phosphorescence lifetimes using an excitation wavelength of 3130 Å. Estimates of the quenching rate constant (units of 1./mole ± sec) are for the cis-isomer, (1.63 ± 0.71) × 1010, quantum yield data, and (2.44 ± 0.11) × 1010, lifetime data; and for the trans-isomer,(2.59 ± 0.09)×1010, lifetime data, and (2.35 ±0.89) × 1010, quantum yield data. An experimentally determined photostationary composition,[cis-C2Cl2H2]/[trans-C2Cl2H2] = 1.8 - 0.1, was in good agreement with a value of 2.00 - 1.15 which was predicted from rate constants derived in this study.

Notes: N2O decay has been monitored via infrared emission for a series of mixtures containing N2O/Ar and N2O/H2/Ar. These mixtures were studied behind reflected shock waves in the temperature interval of 1950-3075°K with total concentrations ranging from 1.2 to 2.5 × 1018 molec/cm3. In all cases the N2O decayed exponentially, and a rate constant kobs was obtained. Runs without added H2 could be described by the following Arrhenius parameters: log A = -9.72 ± 0.08 (in units of cm3/molec · sec) and EA = 203.5 ± 3.6 kJ/mole. Addition of 0.01% and 0.1% H2 was observed to increase the decay rate; the largest increase occurred between 2250 and 2500°K with 0.1% H2, where kobs doubled.Mixtures with no added H2 were analyzed by numerical integration of the following reactions: Quantitative agreement between calculations and observations were obtained with both high and low choices for k2 and k3.The additional reactions were included in the analysis of the mixtures containing H2. Here agreement was obtained only when low values were assigned to k2 and k3. The combinations of k1 ← k3 which agreed with all the data were k1 = 3.25 × 10-10 exp (-215 kJ/RT) and k2 = k3 = 1.91 × 10-11 exp (-105 kJ/RT).

Notes: A competitive technique employing the SO2(3B1) photosensitized isomerization of cis-C2F2H2 to trans-C2F2H2 in the presence of selected fluorinated olefins has been used at 3712 Å and 22°C to determine the quenching rate constants of the reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm SO}_{\rm 2} ({}^3B_1){\rm M}\mathop \to \limits^{k_{_4}}$\end{document} removal. With PSo2 = 25.4 torr and Pcis-C2F2H2 = 0.239 torr Stern-Volmer plots for M = C2H4, C2H2F, 1,1-C2F2H2, C2F4, and C3F6 yielded k4 (units of 1010 l./mole · sec) values of 5.29 ± 0.16, 4.21 ± 0.53, 1.92 ± 0.23, 0.575 ± 0.060, and 0.0335 ± 0.0027, respectively. The results were consistent with the ability of an olefin to quench SO2(3B1) being inversely proportional to the polarizability of the olefin's π bond and the effect can be clearly noted as each H atom in C2H4 is individually replaced by an F atom.

Notes: The kinetics of the proton transfer between hydroxyl ions and phenylazoresorcinol, 4-(p-nitrophenylazo), and 4-(m-nitrophenylazo) resorcinol have been investigated at 25°C and an ionic strength of 0.1M, in a wider pH range than had been done by previous authors. The rate at first decreased with decreasing [OH-], reached a minimum, and then started to increase with decreasing [OH-]. This unusual effect is explained by a mechanism suggested earlier for tropaeolin O. Rate constants and equilibrium constants have been evaluated and discussed.The experimental data were obtained by the T-jump method.

Notes: Measurements of hydroxyl radical (HO) concentrations in ambient air by the technique of laser-induced fluorescence have been recently reported. The present study was undertaken to provide an independent test of the validity of those measurements. A photochemical reactor was used to provide a source of HO, and the concentration of HO in the reactor was determined by the laser-induced fluorescence technique. The HO concentration was also deduced from measured hydrocarbon decay rates in the reactor. There was agreement between the HO concentrations obtained by these two different methods, thus providing further validation of the fluorescence method. Some studies of HO fluorescence efficiency as well as of possible interferences with the fluorescence measurements are reported.

Notes: Explosions occur when O3 and H2CO are mixed in a fresh vessel, even in the presence of several hundred torr of N2 or O2. However, in an aged vessel the reaction is well behaved. The reaction between O3 and H2CO was studied at room temperature in an aged vessel in the presence of about 400 torr of either N2 or O2. The initial rate of O3 decay in the presence of N2 is about 103 times faster than in the presence of O2, and very small amounts of O2 quickly reduce the initial rate of O3 decay in the N2 case. A chain mechanism is postulated to account for the results in which chain initiation can occur both by thermal decomposition of O3, followed by reaction of O(3P) with H2CO to produce HO and HCO, as well as by which may occur both homogeneously and heterogeneously. The rate coefficient k1 ≃ 2.1 × 10-24 cm3/molec · sec represents an upper limit (to within a factor of 2 uncertainty) to the direct gas-phase reaction between O3 and H2CO.

Notes: A combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Br2- in the surrounding aqueous medium. The reaction 3Pmic + Br2aq- → Pmic+ + 2 Br- was followed by optical absorption measurements in the 10-8-10-4-sec range. This reaction possesses a “fast” and a “slow” component with respective rate constants of 2.3 × 106 sec-1 and 1 × 109M-1 · sec-1.The fast component is related to the probability of a Br2- radical meeting a triplet pyrene containing micelle on the first encounter (only 16% of the micelles contained a triplet molecule). Reactions involving more than one Br2- radical-micelle encounter are ascribed to the slow component. The presence of two components reflects the fact that the residence time of a Br2- radical in the vicinity of a cationic micelle is substantially longer than the diffusion time of the radical between micelles. Thus the conditions met in micellar chemistry differ dramatically from those in ordinary solution kinetics where the encounter time is generally much shorter than the time between encounters. Some considerations on the energetics of this electron transfer reaction are also presented.

Notes: The flash photolysis of azomethane in a quartz reaction vessel produces mainly ethane (〉75%) plus smaller quantities of methane, ethylene, and acetylene. The minor products are interpreted quantitatively in terms of methyl radical photolysis at 216 nm to give CH2 and H. This interpretation is substantiated by the dependence of the minor products on flash intensity. The reduction of the ethane yield on adding NO is employed to obtain a rate constant for CH3 + NO as a function of total pressure, based on a value for methyl radical recombination of 4.2 × 10-11 cm3/molec · sec. An RRKM analysis is used to extrapolate the data to give a limiting high-pressure rate constant for CH3 + NO of (1.2 ± 0.1) × 10-11 cm3/molec · sec at 298°K.

Notes: The photolysis of SO2 at 3130 Å, FWHM = 165 Å, and 22°C has been investigated in the presence of cis- and trans-2-pentene. Quantum yields for the SO2 photosensitized isomerization of one isomer to the other have been made for a variation in the [SO2]/[C5H10] ratio of 3.41-366 for cis-2-C5H10 and of 1.28-367 for trans-2-C5H10. A kinetic analysis of each of these systems permitted new estimates to be made for the SO2 collisionally induced intersystem crossing ratio at 3130 Å from SO2(1B1) to SO2(3B1). The estimates of k1a/(k1a + k1b) obtained are 0.12 ± 0.01 and 0.12 ± 0.02 (two different kinetic analyses in the cis-2-C5H10 study) and 0.20 ± 0.05 and 0.20 ± 0.04 (two different kinetic analyses in the trans-2-C5H10 study). Collisionally induced intersystem crossing ratios of k2a/(k2a + k2b) = 0.51 ± 0.10 and k3a/(k3a + k3b) = 0.62 ± 0.12 were obtained for cis- and trans-2-pentene, respectively. Quenching rate constants at 22°C for removal of SO2(3B1) molecules by cis- and trans-2-C5H10 were estimated as (1.00 ± 0.29) × 1011 l./mole·sec and (0.857 ± 0.160) × 1011 l./mole/sec, respectively. Prolonged irradiations, extrapolated to infinite irradiation times, for mixtures initially containing SO2 and pure isomer, either the cis or trans, yielded a photostationary composition of [trans-2-pentene]/[cis-2-pentene] = 2.1 ± 0.1.

Notes: The photochemistry of azoethane and hexafluoroazomethane at 366 nm has been reinvestigated up to 1 atm pressure, and over a range of temperature from 27 to 150°C. The Stern-Volmer type quenching plots primarily demonstrate the decomposition of a single electronic and vibrationally excited state for azoethane, but competitive photodissociation from two different electronic and vibrationally excited states, which was previously postulated for hexafluoroazomethane and azoisopropane, is confirmed for hexafluoroazomethane. It is concluded, however, that two different electronic and vibrationally excited photodissociating states are present in azoethane photolysis, but that one of them is difficult to detect, at least by the present approachPhotosensitization with biacetyl at 436 nm also causes the dissociation of azoethane, and this is probably from the vibrationally equilibrated first triplet state. The energy barrier for this process was found to be 5.0 kcal/mol.