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  • 1
    Electronic Resource
    Electronic Resource
    The translational energy dependence of the F+C2H4 →H+C2H3F reaction cross section near threshold (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 275-284 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have carried out crossed molecular beam studies of the substitution reaction F+C2 H4 →H+C2 H3 F in the collision energy range 0.8–2.5 kcal/mol using a velocity selected F atom beam. The relative substitution cross section is found to decrease with increasing collision energy indicating that if there is a potential energy barrier to F atom addition to C2 H4 it is much less than 0.8 kcal/mol and that the transition state for addition occurs early along the reaction coordinate. These results agree well with ab initio calculations. Although the product translational energy distributions are similar to those obtained from earlier work at higher collision energies, the C2 H3 F angular distributions suggest that a wider range of reactant approach geometries lead to products at lower energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458474
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of endoergic substitution reactions. I. Br+chlorinated aromatic compounds (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6226-6237 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The endoergic substitution reactions Br+R–Cl→Cl+R–Br (R=o-, m-, and p-CH3C6H4, C6H5, C6F5; ΔH°(approximately-equal-to)15 kcal/mol) have been studied using the crossed molecular beams method in the collision energy (Ec ) range 20–35 kcal/mol. The CH3C6H4Br and C6F5Br products were found to be mostly forward scattered with respect to the incident Br beam indicating that the lifetimes of the Br–R–Cl collision complexes are short compared to their rotational periods. The product translational energy distributions and excitation functions for these reactions are well reproduced by statistical calculations that assume that only a few vibrational modes in the collision complexes participate in intramolecular energy redistribution prior to Cl elimination. Ring substituents are found to affect both the extent of energy redistribution in the complexes and the probability of Br addition. For example, no substitution product was observed with m-CH3C6H4Cl or C6H5Cl. The relative magnitudes of the cross sections are explained in terms of possible features of the potential energy surfaces along their reaction coordinates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455439
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamics of endoergic substitution reactions. II. Br+{C2H2Cl2}→Cl+{C2H2ClBr} (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6238-6246 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have extended the crossed beams studies described in the preceding paper to the reactions of Br atoms with 1,1- and trans-dichloroethylene. The shapes of the product translational energy distributions and excitation functions for both reactions support our previous conclusion that Cl elimination from Br–R–Cl collision complexes can compete with Br elimination only in the limit that few vibrational modes of the complex are active in energy redistribution. The substitution cross section for the Br+CH2CCl2 reaction is considerably lower than that for the Br+trans-CHClCHCl reaction in the collision energy range 15–25 kcal/mol, suggesting that steric effects play a dominant role in determining the relative magnitudes of the cross sections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455440
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  • 4
    Electronic Resource
    Electronic Resource
    Crossed molecular beam studies of the reactions of methyl radicals with iodoalkanes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6744-6752 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The I atom exchange reactions, CH3 +RI→CH3 I+R[R=CF3 , (CH3 )3 C], were investigated at a collision energy of (approximate)13 kcal/mol using the crossed molecular beams technique. The supersonic beam of methyl radicals was formed by pyrolyzing a mixture of (approximate)1% di-tert-butyl peroxide in helium in a quartz nozzle. A large fraction of the total energy available to the products from these reactions is channeled into relative translation [(approximate)50% for R=(CH3 )3 C and (approximate)70% for R=CF3 ] suggesting that the dominant interaction among the products is repulsive. The CH3 I product from both reactions was observed to be entirely backward scattered with respect to the incident radical beam indicating that a roughly collinear C–I–C transition state geometry is favored. The present results are compared to those of earlier crossed beam studies of the CH3 +IY→CH3 I+Y(Y=Cl, Br, I) reactions; the differences observed among these reactions are explained with reference to the CH3 I–Y and CH3 I–R interaction potentials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455348
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  • 5
    Electronic Resource
    Electronic Resource
    Comment on: Resonance structure in the energy dependence of state-to-state differential scattering cross sections for the D+H2(v,j)→HD(v',j')+H reaction (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5356-5357 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: During quantum reactive scattering calculations for the title reaction a pronounced resonance structure became apparent in the energy dependence of state−to−state differentialscattering calculations. This resonance structure is explained.(AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459658
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  • 6
    Electronic Resource
    Electronic Resource
    Dissociation of cyclohexene and 1,4-cyclohexadiene in a molecular beam (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4118-4127 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular-beam photofragmentation translational spectroscopy of cyclohexene and 1,4-cyclohexadiene was carried out using 193 nm and IR multiphoton excitation. At 193 nm, both the retro-Diels–Alder reaction of cyclohexene and H2 elimination from both molecules were observed in the ground electronic state, indicating the occurrence of internal conversion from the initially excited electronic states. The retro-Diels–Alder reaction is shown to be concerted up to an internal energy higher than 148 kcal/mol. Hydrogen-atom elimination was also observed for both molecules following 193 nm excitation. The H atom is eliminated from an excited state of cyclohexene and is assigned to be from a carbon adjacent to the double bond, with a corresponding C–H bond energy of 87±3 kcal/mol. It is shown that the peak of the translational energy distribution for concerted dissociation in the ground state is determined mainly by the dynamics of the potential-energy release along the reaction coordinate, and is not sensitive to either the amount of internal energy or the form of excitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456841
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  • 7
    Electronic Resource
    Electronic Resource
    COINCIDENCE SPECTROSCOPY (2001)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 52 (2001), S. 165-192 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The application of coincidence techniques to the study of the reaction dynamics of isolated molecules is reviewed. Coincidence spectroscopy is a powerful approach for carrying out a number of measurements. At its most basic level, coincidence techniques can identify the source of a specific signal, as in the well-known photoelectron-photoion coincidence approach used for several years. By carrying out coincidence experiments in an increasingly differential manner, correlated energy and angular distributions of reaction products may be recorded. Completely energy- and angle-resolved measurements of photoelectrons and ionic or neutral products can reveal molecular-frame photoelectron and photofragment angular distributions and aid in the characterization of dissociative states of molecules and ions. Recent work in this area is reviewed, including examples from studies of dissociative photodetachment, dissociative photoionization, time-resolved studies of dissociative photoionization, and three-body dissociation processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physchem.52.1.165
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  • 8
    Electronic Resource
    Electronic Resource
    Multiple-ion-beam time-of-flight mass spectrometer (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 3386-3389 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An innovative approach to increase the throughput of mass spectrometric analyses using a multiple-ion-beam mass spectrometer is described. Two sample spots were applied onto a laser desorption/ionization target and each spot was simultaneously irradiated by a beam of quadrupled Nd:YLF laser radiation (261.75 nm) to produce ions by laser-desorption ionization. Acceleration of the ions in an electric field created parallel ion beams that were focused by two parallel einzel lens systems. After a flight path of 2.34 m, the ions were detected with a microchannel plate-phosphor screen assembly coupled with a charge coupled device camera that showed two resolved ion beams. Time-of-flight mass spectra were also obtained with this detector. Experiments were performed using both metal atom cations (Ti+ and Cr+) produced by laser desorption/ionization and the molecular ions of two different proteins (myoglobin and lysozyme), created by matrix assisted laser desorption/ionization using an excess of nicotinic acid as matrix. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1380682
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  • 9
    Electronic Resource
    Electronic Resource
    Predissociation dynamics of formyloxyl radical studied by the dissociative photodetachment of HCO2−/DCO2−+hν→H/D+CO2+e− (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5345-5348 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociative photodetachment (DPD) of HCO2− and DCO2− was studied at 258 nm. State-resolved translational energy distributions were observed correlated to bending excitation in the CO2 product for the channel producing H/D+CO2, indicating very low rotational excitation in the products consistent with predissociation of a C2ν HCO2 molecule. No evidence was found for dissociation into OH+CO. All three low-lying electronic states (2A1, 2B2, and 2A2) were found to dissociate, but resolved progressions were only observed from photodetachment to the 2A1 and 2B2 states. Photoelectron-photofragment coincidence spectra for DCO2− show resolved vertical bands and indicate that multiple CO2 vibrational states are accessible from each vibrational level in the predissociating DCO2 molecule. The resolved structure is assigned to vibrational predissociation sequence bands, observable in this DPD process owing to the dissociation dynamics and the near degeneracy of the vibrational levels in the 2A1 and 2B2 states of HCO2 and the bending mode of the CO2 products. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1404143
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  • 10
    Electronic Resource
    Electronic Resource
    Dissociative photodetachment studies of O−(H2O)2, OH−(H2O)2, and the deuterated isotopomers: Energetics and three-body dissociation dynamics (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8436-8444 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoelectron–photofragment coincidence spectroscopy was used to study dissociative photodetachment of the doubly hydrated clusters of oxide and hydroxide, M−(H2O)2→M+2H2O+e− (M=O, OH). These experiments yield information on the energetics of the parent anion and the dissociation dynamics of the photodetached neutral species. Photoelectron spectra and photoelectron–photofragment coincidence spectra are presented and compared to data for O−(H2O) and OH−(H2O). Unlike the singly hydrated species, no evidence of vibrationally resolved product translational energy distributions is observed. The second hydration energy of O− with both H2O and D2O was also measured to be 0.80±0.08 and 0.81±0.08 eV, respectively. The three-body dissociation dynamics of the neutral clusters produced by photodetachment were studied by measuring the velocities and recoil angles of all the particles in coincidence. The observed partitioning of momentum is consistent with a two-step mechanism or dissociation from a wide range of starting geometries. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1366332
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