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Trajectory surface-hopping study of methane photodissociation dynamics
Maricris D Lodriguito1, György Lendvay, George C Schatz
1Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
The Journal of Chemical Physics
|December 17, 2009
Summary
Nonadiabatic dynamics are crucial for understanding methane photodissociation, revealing key product channels like CH3+H and CH2+H2. These findings align well with experimental observations of methane dissociation products.
Area of Science:
- Physical Chemistry
- Theoretical Chemistry
- Spectroscopy
Background:
- Methane photodissociation is a fundamental process in atmospheric and combustion chemistry.
- Understanding the excited state dynamics of methane is key to predicting its reactivity.
- Previous studies have provided experimental insights into methane dissociation products.
Purpose of the Study:
- To investigate the photodissociation of methane on its lowest singlet excited state (1 (1)T(2)) at 122 nm.
- To elucidate the role of nonadiabatic dynamics in methane dissociation.
- To analyze product state branching and energy partitioning in detail.
Main Methods:
- Employed the fewest switches nonadiabatic trajectory surface hopping approach.
- Utilized CASSCF(8,9) calculations with an aug-cc-pvdz basis set for trajectories and couplings.
- Simulated dissociation pathways and analyzed product distributions.
Main Results:
- Identified CH3(X 2A2)+H and CH2(a 1A1)+H2 as major dissociation channels, consistent with experiments.
- Demonstrated the importance of nonadiabatic dynamics, including surface hopping and Renner-Teller induced internal conversion.
- Observed a roaming atom mechanism in approximately 5% of trajectories, contributing to product diversity.
Conclusions:
- Nonadiabatic effects significantly influence methane photodissociation pathways and product distributions.
- The theoretical model accurately reproduces experimentally observed branching fractions and energy distributions.
- Intersystem crossing is not essential for explaining the primary dissociation behavior.
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