Trajectory surface-hopping study of methane photodissociation dynamics

Journal Article · Mon Dec 14 00:00:00 EST 2009 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3271242· OSTI ID:21559816

Lodriguito, Maricris D; Schatz, George C ^[1]; Lendvay, Gyoergy ^[2]

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1. Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113 (United States)
2. Chemical Research Center, Hungarian Academy of Sciences, H-1525 Budapest, P. O. Box 17 (Hungary)

We use the fewest switches nonadiabatic trajectory surface hopping approach to study the photodissociation of methane on its lowest singlet excited state potential surface (1 {sup 1}T{sub 2}) at 122 nm, with emphasis on product state branching and energy partitioning. The trajectories and couplings are based on CASSCF(8,9) calculations with an aug-cc-pvdz basis set. We demonstrate that nonadiabatic dynamics is important to describe the dissociation processes. We find that CH{sub 3}(X-tilde{sup 2}A{sub 2}{sup ''})+H and CH{sub 2}(a-tilde{sup 1}A{sub 1})+H{sub 2} are the major dissociation channels, as have been observed experimentally. CH{sub 3}+H is mostly formed by direct dissociation that is accompanied by hopping to the ground state. CH{sub 2}+H{sub 2} can either be formed by hopping to the ground state to give CH{sub 2}(a-tilde{sup 1}A{sub 1})+H{sub 2} or by adiabatic dissociation to CH{sub 2}(b-tilde{sup 1}B{sub 1})+H{sub 2}. In the latter case, the CH{sub 2}(b-tilde{sup 1}B{sub 1}) can then undergo internal conversion to the ground singlet state by Renner-Teller induced hopping. Less important dissociation mechanisms lead to CH{sub 2}+H+H and to CH+H{sub 2}+H. Intersystem crossing effects, which are not included, do not seem essential to describe the experimentally observed branching behavior. About 5% of trajectories involve a roaming atom mechanism which can eventually lead to formation of products in any of the dissociation channels. Branching fractions to give H and H{sub 2} are in good agreement with experiment, and the H atom translational energy distribution shows bimodal character which also matches observations.

• OSTI ID: 21559816
• Journal Information: Journal of Chemical Physics, Vol. 131, Issue 22; Other Information: DOI: 10.1063/1.3271242; (c) 2009 American Institute of Physics; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ATOMS
BRANCHING RATIO
DISSOCIATION
ENERGY SPECTRA
EXCITED STATES
GROUND STATES
HYDROGEN
INTERNAL CONVERSION
METHANE
PHOTOLYSIS
PHOTON-MOLECULE COLLISIONS
POTENTIAL ENERGY
REACTION KINETICS
SURFACES
SWITCHES
TRAJECTORIES
ALKANES
CHEMICAL REACTIONS
COLLISIONS
CONVERSION
DECAY
DECOMPOSITION
DIMENSIONLESS NUMBERS
ELECTRICAL EQUIPMENT
ELEMENTS
ENERGY
ENERGY LEVELS
EQUIPMENT
HYDROCARBONS
KINETICS
MOLECULE COLLISIONS
NONMETALS
NUCLEAR DECAY
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTON COLLISIONS
SPECTRA