Ab initio calculations of vibronic spectra and dynamics for small polyatomic molecules: Role of Duschinsky effect

The Duschinsky effect has been shown to be significant in spectroscopy and dynamics of molecules that involve the pi-pi* transitions. In this paper, w e present a derivation of exact expressions for optical absorption and radi ationless transitions in polyatomic molecules with displaced-distorted-rota ted harmonic potential surfaces. In the formulation, we take into account t he temperature effect exactly. The application of this new formulation is d emonstrated for ethylene and allene, where the Duschinsky effect in the fir st singlet excited electronic state is very strong.