ASPECTS OF DISSIPATIVE ELECTRONIC AND VIBRATIONAL DYNAMICS OF STRONGLY VIBRONICALLY COUPLED SYSTEMS

The intramolecular non-Born-Oppenheimer quantum dynamics on conically intersecting potential-energy surfaces is analyzed on the basis of exact (numerical) time-dependent quantum calculations for two representative two-state three-mode vibronic-coupling models. A compact description of the time-dependent dynamics in terms of reduced density matrices of the electronic and vibrational subsystems is introduced. Results are presented for the time evolution of electronic and vibrational coherences, populations, as well as subsystem entropies. It is found that such simple two-state three-mode vibronic coupling models exhibit a rich variety of dissipative phenomena on femtosecond time scales. The numerical results reveal an interesting interplay of driven electronic surface-hopping processes and dephasing of coherent vibrational motion which is presumably a generic feature of ultrafast internal conversion processes in polyatomic molecules. © 1990 American Institute of Physics.