anion: A semiclassical molecular dynamics simulation method

In this paper we describe a new semiclassical method for simulating femtosecond pump–probe photoelectron spectroscopy, and its implementation to study the excited state photodissociation dynamics of the I2 2 anion. Our algorithm involves a forward–backward ~FB! semiclassical ~SC! initial value representation ~IVR! method for calculating the time dependent photodetachment spectrum P(e ,Dt) as a function of the kinetic energy e of the photodetached electron and the delay time Dt between the pump and probe pulses. We describe the radiation-chromophore interaction perturbatively to first order in both pulse fields, assuming the Condon approximation for the electronic transition dipole moments. Our computed spectra are in excellent agreement with full quantum mechanical simulations. © 1999 American Institute of Physics. @S0021-9606~99!00107-5#