Forward-backward semiclassical calculation of spectral line shapes:: I2 in a rare gas cluster

The forward-backward semiclassical representation introduced by Makri and Thompson (Chem. Phys. Lett. 1998, 291, 101-109.) is employed to evaluate dipole correlation functions for electronic transitions of molecules in clusters 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 spectrum is dominated by the short-time dynamics of the system, a factorization of the stability matrix entering the semiclassical expression of the propagator provides an excellent approximation, substantially reducing the computational cost.