Close-coupling wave-packet study of He and Ne sticking on metal surfaces

A fully quantum-mechanical study is made of light particles sticking on a model Cu surface. The full molecule-metal wave function is expanded to include states corresponding to elastic scattering and the creation or annihilation of single phonons. The coupled-channel equations for this system are evolved in time numerically using well-known wave-packet techniques. For light particles and low energies, where only single-phonon interactions are important, this is a rigorous treatment of the dynamics and can serve as a benchmark. Probability distributions for energy transfer are computed from the reduced density matrix. These distributions exhibit resonances which correspond to transitions into the gas-metal bound states. The trapping probability is studied as a function of particle mass, energy, and surface temperature for a flat Cu surface. A comparison is made with the forced oscillator model and other approximate methods which are shown to give poor results for the sticking probability of light particles.