High-resolution inelastic He-atom surface scattering experiments have been carried out on an in situ cleaved KCN(001) molecular crystal surface in the temperature range of 40<T<334 K covering the temperature range of the two known bulk phase transitions at 168 and 83 K. No Bragg diffraction peaks other than the specular beam are observed over the entire temperature range. The scattering intensity is primarily composed of inelastic multiphonon processes along with some diffuse elastic-scattering contributions, the latter of which increases in magnitude with decreasing temperature while the former decreases in intensity with decreasing temperature. A theoretical model developed for explaining the multiphonon-scattering process gives very good quantitative agreement with the data.

• Received 10 July 1995

DOI:https://doi.org/10.1103/PhysRevB.52.14185