Multiple time scale population transfer-dynamics in coupled electronic states

•Two time-scales for vibronic population transfer are identified.•Rabi-like oscillations can be induced through constant vibronic coupling.•Population transfer is influenced by quantum phases.

We regard the wave-packet dynamics in two electronic states which interact via a constant coupling element. Performing numerical calculations it is found that the time-dependent populations exhibit oscillatory variations with two characteristic periods. Whereas, as expected, one period is determined by the vibrational motion, it is shown that Rabi-type oscillations occur which are influenced by the parameters of the potential energy curves, the coupling and the amplitudes in the two states on one hand, and by the nuclear motion on the other. An analysis of the numerical results is performed within various levels of approximation.