Rainbow scattering of CH4 and C2H6 molecular beams from a LiF(001) surface: Dependence on incident kinetic energy and molecular anisotropy

Angular intensity distributions of CH4 and C2H6 molecules scattered from a highly corrugated LiF(001) surface have been measured in high resolution. C H4 molecules reveal clear rainbow scattering, while C2H6 molecules do not. This difference is attributed to the structural anisotropy between these mo lecules; a CH4 molecule is more spherically symmetric than a C2H6 molecule. The microscopical repulsive potential, corrugation of the LiF(001) surface experienced by these molecules is found to decrease as the incident kineti c energy increases. This counterintuitive lessening of the corrugation is a consequence of the potential surface arising from two very different sized substrate ions. (C) 2001 American Vacuum Society.