Abstract

The elastic theory for resonant atom-surface scattering is shown to explain simply the occurrence of both minima and maxima at resonance and the strength and shape of the absorption lines, on the assumption that the repulsive part of the potential is of the form V(z−ζ), where ζ is the surface corrugation and V can be regarded as a hard wall at the locus of turning points. Explicit formulae are obtained in the semiclassical limit. For a simple sinusoidal corrugatrion with rectangular symmetry, the signature of an isolated resonance is determined unambiguously by the parity of ¦m¦+¦m' − m¦−¦m'¦+¦n¦+¦n' −n¦ s|n'¦, where (m,n) is the resonant vector and (m',n') the scattering vector, in reciprocal lattice units. The predicted signatures of isolated resonances agree with experiments and more elaborate calculations for the systems He/LiF and He/Graphite. Calculated splittings in the surface band structure also show reasonably good agreement. An alternative formulation of resonant scattering, as suggested by Wolfe and Weare, can be based in an appropriate sorting of successive orders of distorted wave perturbation theory. For small corrugations there is good correspondence between the two approaches.