Classical description of ultrafast internal conversion processes. The benzene cation

Abstract

Based on the classical electron analog model due to Meyer and Miller, a classical approach to the microscopic modelling of ultrafast internal conversion processes in polyatomic molecules is outlined. Adopting a recently proposed multimode model of the X̃ 2E 1g, B̃ 2E 2g and C̃ 2A 2u electronic states of the benzene cation (Köppel), we present computational studies on the C̃→B̃→X̃ electronic relaxation process in this molecular system. The classical model is shown to be in semi-quantitative agreement with quantum mechanical five-mode reference calculations, reproducing nicely transient features as well as long-time limits of the diabatic electronic population probabilities. Including the remaining important vibrational modes and vibronic interactions of the benzene cation into the model description, the classical simulations predict internal conversion decay times of T B̃C̃≈6 fs for the C̃→B̃ and T x̃B̃ ≈ 42 fs for the B̃ → X̃ transition.