Forward-backward semiclassical calculation of spectral line shapes: I-2 ina rare gas cluster

The forward-backward semiclassical representation introduced by Makri and T hompson (Chem. Phys. Lett. 1998, 291, 101-109.) is employed to evaluate dip ole correlation functions for electronic transitions of molecules in cluste rs or the condensed phase. The method is applied to the X --> B transition of an iodine molecule in a host of argon atoms. In this case, where the spe ctrum is dominated by the short-time dynamics of the system, a factorizatio n of the stability matrix entering the semiclassical expression of the prop agator provides an excellent approximation, substantially reducing the comp utational cost.