Molecular dynamics of non-equilibrium infrequent events: Laser- induced desorption from surfaces.

An obvious shortcoming of classical trajectory simulations of chemical reactions is their limitation to short timescale processes. While procedures to extend simulations to long timescales have been developed for reactions occurring under equilibrium conditions, there are no analogous techniques for nonequilibrium situations. We propose such a method which, although not rigorous, is simple, practical and appears to give results of useful accuracy. We illustrate the method by simulating infra-red laser-induced desorption of an atom from a solid surface. At vanishingly low laser powers, desorption rate constants agree with those calculated by standard equilibrium infrequent event methods. They also agree at high laser powers with the values obtained from direct simulation in the fast timescale limit. At intermediate powers they are in accord with the results of a master-equation treatment described in the Appendix.