ABSTRACT
Chemical reaction dynamics [1] can often be described in the framework of the Born-Oppenheimer approximation as the evolution from reactants to products on a single adiabatic potential energy surface (PES). However, this approximation may become invalid if the relevant PES happens to be energetically close to another one, for example near a conical intersection [2], in which case nonadiabatic transitions between these electronic states become likely [3]. Reaction dynamics on coupled PESs is governed by two quantum effects: (i) population transfer from one electronic state to another, and (ii) phase coherence between the nuclear wave packets evolving on each state, with these two effects reciprocally influencing each other. Therefore, nonadiabatic dynamics is a highly nonclassical process, which must be treated quantum mechanically. Various methods have been proposed to describe the concerted motion of nuclei on coupled electronic states and we refer the reader to Burghardt and Cederbaum [4] for a recent bibliography. In this chapter, we introduce and discuss a formally exact description of nonadiabatic dynamics using quantum trajectories.
