Multi-dimensional mixed quantum-classical description of the laser-induced desorption of molecules

A mixed quantum-classical method for the simulation of laser-induced desorption processes at surfaces is implemented. In this method, the nuclear motion is described classically, while the electrons are treated quantum mechanically. The feedback between nuclei and electrons is taken into account self-consistently. The computational efficiency of this method allows a more realistic multi-dimensional treatment of desorption processes. We apply this method to the laser-induced desorption of NO from NiO(100) using a two-state two-dimensional potential energy surface derived from ab initio quantum chemical calculations; we extend this potential energy surface to seven dimensions employing a physically reasonable model potential. By comparing our method to jumping wave-packet calculations on exactly the same potential energy surface we verify the validity of our method. We focus on the velocity, rotational, and vibrational distributions of the desorbing NO molecules. Furthermore, we model the energy transfer to the substrate by a surface oscillator. Including recoil processes in the simulation has a decisive influence on the desorption dynamics, as far as the velocity and rotational distribution is concerned. In particular, the bimodality in the velocity distribution observed in low dimensions and in the experiment disappears in a high-dimensional treatment.