Application of the frozen Gaussian approximation to the photodissociation of CO2

The semiclassical frozen Gaussian approximation of Herman and Kluk is compared with exact quantum mechanical wavepacket propagation for the collinear photodissociation of CO2. The approximation is found to be quantitatively accurate even at long times, and to reproduce all of the dynamical features in the absorption spectrum. However, the statistical errors in the Monte Carlo integration over the initial phase space are found to degrade with time and to demand an increasingly large number of sample points for longer times. The reasons for this numerical difficulty are discussed.