A non-adiabatic dynamics study of octatetraene: The radiationless conversion from S{sub 2} to S{sub 1}
- Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry of the Ministry of Education (MOE), School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093 (China)
Simulation of the excited state dynamics of all-trans-1,3,5,7-octatetraene has been performed to investigate the ultrafast radiationless S{sub 2} → S{sub 1} internal conversion process. Multireference configuration interaction with single excitation method has been employed to optimize the equilibrium structure of the excited states, as well as the S{sub 2}/S{sub 1} conical intersection, and to investigate the non-adiabatic molecular dynamics of the S{sub 2}/S{sub 1} state transition. At the conical intersection, the molecule is found to be distorted from the original planar trans structure to a nearly perpendicular conformation around C{sub 3}−C{sub 4} bond, with the torsion angle being about 107°. Such structural change can result in mutual approaching of states S{sub 2} and S{sub 1} in energy, and drastically increase the nonadiabatic coupling between the two states by destroying the inter-state symmetry prohibition in the electronic wavefunctions. Surface-hopping molecular dynamics simulations are performed to describe the non-adiabatic process. Upon the Franck-Condon excitation to the S{sub 2} state, the molecule quickly twists its C{sub 3}−C{sub 4} bond and approaches the conical intersection region, where it can undergo efficient internal conversion to S{sub 1}. The decay time constant (τ) of S{sub 2} state is estimated to be around 251 fs by fitting the occupation number of average fraction of trajectories using an exponential damping function. This value is reasonably consistent with previous experimental measurements of around 300–400 fs.
- OSTI ID:
- 22253229
- Journal Information:
- Journal of Chemical Physics, Vol. 139, Issue 24; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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