HOT-ELECTRON MEDIATED PHOTODESORPTION - A TIME-DEPENDENT APPROACH APPLIED TO NO/PT(111)

Time-dependent quantum wave packets have been used in a model calculation to investigate the substrate-mediated photodesorption of a molecule from a metal surface. A "hot" electron, generated in the substrate by an absorbed photon, temporarily resonates in an unoccupied molecular orbital. This results in a new set of forces, and if the electron spends sufficient time in the resonance, then on returning to the electronic ground state the molecule will have acquired sufficient energy to desorb. Rather than modeling the excitation and relaxation steps independently, we treat the motion of the molecule and the hot electron on an equal footing. We have studied the dynamics on potential energy surfaces (PESs) explicitly including both the electronic and nuclear coordinates. PES parameters were chosen to model NO desorption from Pt where it has been suggested that the excited state is attractive. The desorption probability has been calculated as a function of hot electron energy and photon energy for different potential topologies. We show that observable desorption is possible for short resonance lifetimes (∼1 fs) and moderate excited state potential gradients. Also presented are the translational energy distributions of the desorbing molecules. © 1995 American Institute of Physics.