Intramolecular and Surface Vibratory Modes of Butane Adsorbed on Graphite Observed by Inelastic Neutron Scattering

Inelastic and elastic neutron scattering have been used to study the dynamics and structure of butane (${\mathrm{C}}_4$ ${\mathrm{H}}_{10}$) adsorbed on a graphitized carbon powder at 77 K. In addition to the intramolecular vibrations found in the bulk solid, new surface vibratory modes are observed. A simple model which fits the principal features of the monolayer excitation spectrum suggests an orientation of the adsorbed butane molecule and the location and strength of the bonds to the substrate.