Semiquantum Expressions for Electronically Nonadiabatic Electron Ejection Rates

Abstract

Molecular anions that possess excess internal vibrational and/or rotational energy can eject their “extra” electron through a radiationless transition event involving non-Born-Oppenheimer coupling. In such processes, there is an interplay between the nuclear motions (i.e., vibrations and rotations) and the electronic motions that allows energy to be transferred from the former to the latter and that permits momentum and/or angular momentum to also be transferred in a manner that preserves total energy, momentum, and angular momentum. There are well-established quantum mechanical expressions for the state-to-state rates of this kind of radiationless process, and these expressions have been used successfully to compute electron ejection rates. In this paper, we recast the quantum rate equations by making use of approximations that have proven useful in rewriting the quantum expressions for rates of photon absorption in a more classical manner. In so doing, our goal has been to produce rate expressions that allow one to understand, in a more nearly classical manner, the energy-transfer process and to more readily predict when such rates will be significant.