On the quasiadiabatic description of the dynamics of electronically adiabatic chemical reactions

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Abstract
We present a description and analysis of electronically adiabatic chemical reactions in terms of nonadiabatic basis sets. By using an orthogonal transformation we separate the Hamiltonian into reactive and nonreactive parts. Explicit expressions are given for the reactive part of the interaction and some conditions are discussed for expressing it in terms of Franck–Condon type nuclear overlap. Next we derive closed formal expressions for all the various cross sections (elastic, inelastic, and reactive) in a chemically reactive system. With the present approach we make a distinction between the Franck–Condon and first‐order approximation in the reactive interaction. Closed expressions for all the cross sections in terms of finite‐size matrices are derived by making use of the K matrix formalism. These expressions enable us to use the Franck–Condon approximation and at the same time retain reactive interactions to infinite order.