Photodissociation of benzene under collision-free conditions: An ab initio/Rice-Ramsperger-Kassel-Marcus study

Kislov, V. V., Nguyen, T. L., Mebel, A. M., Lin, S. H. and Smith, S. C. (2004) Photodissociation of benzene under collision-free conditions: An ab initio/Rice-Ramsperger-Kassel-Marcus study. Journal of Chemical Physics, 120 15: 7008-7017. doi:10.1063/1.1676275

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Author Kislov, V. V.
Nguyen, T. L.
Mebel, A. M.
Lin, S. H.
Smith, S. C.
Title Photodissociation of benzene under collision-free conditions: An ab initio/Rice-Ramsperger-Kassel-Marcus study
Journal name Journal of Chemical Physics   Check publisher's open access policy
ISSN 0021-9606
Publication date 2004-04
Sub-type Article (original research)
DOI 10.1063/1.1676275
Open Access Status File (Publisher version)
Volume 120
Issue 15
Start page 7008
End page 7017
Total pages 10
Place of publication Lancaster, Pa.
Publisher American Institute of Physics
Collection year 2004
Language eng
Subject C1
250603 Reaction Kinetics and Dynamics
780103 Chemical sciences
0399 Other Chemical Sciences
Abstract The ab initio/Rice-Ramsperger-Kassel-Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of benzene at various wavelengths upon absorption of one or two UV photons followed by internal conversion into the ground electronic state. Reaction pathways leading to various decomposition products have been mapped out at the G2M level and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for C6H5+H, C6H4+H-2, C4H4+C2H2, C4H2+C2H4, C3H3+C3H3, C5H3+CH3, and C4H3+C2H3 have been calculated subsequently using both numerical integration of kinetic master equations and the steady-state approach. The results show that upon absorption of a 248 nm photon dissociation is too slow to be observable in molecular beam experiments. In photodissociation at 193 nm, the dominant dissociation channel is H atom elimination (99.6%) and the minor reaction channel is H-2 elimination, with the branching ratio of only 0.4%. The calculated lifetime of benzene at 193 nm is about 11 mus, in excellent agreement with the experimental value of 10 mus. At 157 nm, the H loss remains the dominant channel but its branching ratio decreases to 97.5%, while that for H-2 elimination increases to 2.1%. The other channels leading to C3H3+C3H3, C5H3+CH3, C4H4+C2H2, and C4H3+C2H3 play insignificant role but might be observed. For photodissociation upon absorption of two UV photons occurring through the neutral hot benzene mechanism excluding dissociative ionization, we predict that the C6H5+H channel should be less dominant, while the contribution of C6H4+H-2 and the C3H3+C3H3, CH3+C5H3, and C4H3+C2H3 radical channels should significantly increase. (C) 2004 American Institute of Physics.
Keyword Physics, Atomic, Molecular & Chemical
Quadratic Configuration-interaction
Vacuum Ultraviolet Photolysis
Potential-energy Surface
Coupled-cluster Singles
Rate Constants
Propargyl Radicals
Hot Benzene
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 04:10:21 EST