Theory of resonant inelastic one-phonon scattering of He atoms from a LiF(001) single crystal surface

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For the He–LiF(001) system, molecular beam measurements of the inelastically scattered intensity have revealed a large number of resonance structures. In this paper the theoretical description of these resonant inelastic one-phonon scattering processes is provided in the framework of the distorted wave Born approximation. In the first step the elastic diffractive scattering problem is solved exactly using close coupling calculations for a recently developed pairwise additive semi ab initio potential and a rigid lattice. As the potential contains both the attractive well and the corrugation in a realistic manner, bound state resonances are fully taken into account. In the next step the inelastic coupling due to one-phonon processes is treated as a perturbation of the elastic wave functions obtained from the close coupling solutions. The inelastic coupling potential is the same semi ab initio two-body potential used to describe the atom–static surface potential, and the LiF–surface lattice dynamics are described by realistic Green’s function calculations. The theoretical results provide a good description of most of the structures seen in experimental angular distributions and time of flight spectra. The resonant features can be interpreted in terms of one-phonon assisted adsorption into and desorption out of specified bound states of the atom–surface potential. In addition to the contributions of Rayleigh phonons the bulk phonons contribute about 40% to both the creation and annihilation inelastic scattering processes.