A NEW SEMICLASSICAL INITIAL-VALUE METHOD FOR FRANCK-CONDON SPECTRA

A new semiclassical initial value method is derived for the calculatio n of bound-bound Franck-Condon spectra. The method combines the frozen Gaussian approximation of Herman and Kluk with the cellular dynamics algorithm of Heller, taking advantage of the best features of both app roaches. In particular, it is immune to both the problems associated w ith chaotic trajectories that are encountered in the Herman-Kluk metho d and the problems associated with caustic singularities that can be e ncountered in the cellular dynamics method. Example applications to so me model two- and three-dimensional bound state problems show that the new method is both accurate and efficient, and moreover that the effo rt that is required to calculate a bound-bound Franck-Condon spectrum semiclassically does not appear to increase significantly with the dim ensionality of the problem.