Low-energy methane scattering from Pt(111).

We have measured the temperature dependence of angular distributions of CH4 from Pt(111) at an incident energy of 109 meV. A broad angular distribution has been observed along the two main symmetry directions, whereby the peak center shifts from the supra-specular position to the sub-specular position when the surface temperature increases from 120 K to 800 K. Different widths have been measured for the scattering patterns along the [ 1¯01 ] and the [ 2¯11 ] azimuthal directions. Based on calculations performed within the binary collision model, these differences have been ascribed to different corrugations of the CH4-Pt(111) interaction potential along the two high-symmetry directions. This corrugation has been estimated from the model calculations to amount ∼0.03 Å, a factor of three larger than the one measured with helium diffraction.