Inelastic rainbow scattering of CH4 molecules from a LiF(001) surface

Angular intensity and velocity distributions of CH4 scattered from a LiF(001) surface have been measured using CH4 molecular beams with energies in the range of E-i = 190-570 meV. Rainbow scattering of CH4 molecules has been obtained for the [100] incident azimuthal direction and the results are compared with the "Washboard" model proposed by Tully [J. Chem. Phys. 92 (1990) 680]. A qualitative agreement between our experimental results and the model has been observed as far as the dependence of angular intensity distribution of scattered CH4 molecules on both incident energy and surface temperature are concerned. It is found that the attractive potential acting on CH4 at the LiF surface plays an important role in determining the rainbow peak position. The model also explains the angular velocity distribution of scattered CH4 molecules.