Classical dynamics of impulsively driven collisional energy transfer

This paper seeks to address the problem of collisional energy transfer between atoms or molecules arranged in connecting layers on a solid surface in response to impulsive photon impact. An analysis based on classical trajectories of the motions of a line of touching spheres subject to impact at one end, computed by Green's method, is adopted to describe the collisional behavior of atoms or molecules attached to a metal subsequent to electronic excitation by an ultrafast laser pulse. To highlight the essential dynamics, the characteristic line dissociation and rebound behavior of a series of connected spheres is investigated for different impact durations, amplitudes. and numbers of particles. The individual particle trajectories reveal the propagation of a disturbance along the line which results in fragmentation of the outermost particles from the remainder. In applying this scheme to energy transfer between molecules stacked on a low-temperature metal, a model of photon-induced, resonant electron scattering between displaced harmonic oscillators is invoked to estimate the magnitude of the impulsive force that acts on the atoms or molecules immediately adjacent to the solid surface. From the time-dependent line fragmentation velocities, kinetic energy distributions are calculated for photodesorption of benzene molecules from Pt{111} by a normally incident laser beam, and are compared with recent experimental measurements.