Scattering of molecules by a crystal surface

A theoretical study of scattering of gas molecules by a crystal surface is reported. According to the lattice vibration, the problem is divided into elastic scattering and inelastic scattering. The elastic scattering is treated in detail. The Fourier components of the surface field of He above a LiF crystal are calculated in order to obtain the diffracted patterns numerically. A resonance phenomenon of the molecular state on the surface is discussed, and the resonant energy and lifetime of the resonant state are obtained by use of Frisch and Stern's data.