A classical model for time- and frequency-resolved spectroscopy of nonadiabatic excited-state dynamics

Abstract

Based on the framework of the classical electron analog due to Meyer and Miller, we outline a new classical formulation of the spectroscopy of nonadiabatically coupled electronic states. The time-dependent molecular correlation functions are expressed in terms of the classical dipole function that is the classical analog of the quantum-mechanical electronic dipole operator. Explicit expressions for cw absorption and for time- and frequency-resolved pump—probe spectra are derived. The capability of the classical method is illustrated by computational results for a four-mode model of the S 2-S 1 conical intersection in pyrazine. Comparison to exact quantum-mechanical calculations reveals that the classical model reproduces the qualitative features of the cw absorption and the time- and frequency-resolved spectra.