A uniform classical S matrix theory for bound-bound Franck-Condon factors

A uniform classical S matrix theory of bound-bound Franck-Condon factors is developed and applied to a model non-separable potential system with two degrees of freedom. Comparison with exact quantum results shows the method to be substantially more accurate than the Heller frozen gaussian approach, although the latter gives acceptable accuracy for many purposes and also has advantages of flexibility and ease of operation.