Quantum dynamics at a conical intersection: The role of the variation of oscillator frequencies in the diabatic transition

The role of frequency variation in the transition between two crossing diabatic electronic states originating in a conical intersection is studied. We have considered a minimal model with two vibrational degrees of freedom, a coupling mode, and a tuning mode, and performed computations varying the frequency of both in the initially unoccupied diabatic state. It is shown that neglecting this effect may result in a wrong estimate of the transition probability. Two simple rules for evaluating qualitatively such an effect are proposed. (C) 1898 American Institute of Physics. [S0021-9606(98)02044-3].