Laser-driven coupled electron-nuclear dynamics: Quantum mechanical simulation of molecular photodesorption from metal films

摘要

In this paper we report dynamical simulations of laser-driven, coupled nuclear-electron dynamics for a molecule-surface system. Specifically, the laser desorption of a small molecule (NO) from a metal slab (Pt) in the so-called DIET limit (Desorption Induced by Electronic Transitions), is studied. The excitation of the metal electrons by a laser pulse followed by the formation of a negative ion resonance, its subsequent decay, and the simultaneous desorption of the molecule are all treated within a single quantum mechanical model. This model is based on an earlier theory of Harris and others [S. M. Harris, S. Holloway, and G. R. Darling, J. Chem. Phys. 102, 8235 (1995)], according to which a nuclear degree of freedom is coupled to an electronic one, both propagated on a single non-Born-Oppenheimer potential energy surface. The goals of the present contribution are (ⅰ) to make a conceptual connection of this model to the frequently adopted nonadiabatic "multi-state" models of photodesorption, (ⅱ) to understand details of the desorption mechanism, (ⅲ) to explicitly account for the laser pulse, and (ⅳ) to study the photodesorption as a function of the thickness of the metal film, and the laser parameters. As an important methodological aspect we also present a highly efficient numerical scheme to propagate the wave packet in a problem-adapted diabatic basis.