SCATTERING OF HE ATOMS FROM KCN(001) - ANALYSIS OF THE ENERGY-EXCHANGE

High-resolution inelastic He-atom surface scattering experiments have been carried out on an in situ cleaved KCN(001) molecular crystal surf ace in the temperature range of 40 < T < 334 K covering the temperatur e range of the two known bulk phase transitions at 168 and 83 R. No Br agg diffraction peaks other than the specular beam are observed over t he entire temperature range. The scattering intensity is primarily com posed of inelastic multiphonon processes along with some diffuse elast ic-scattering contributions, the latter of which increases in magnitud e with decreasing temperature while the former decreases in intensity with decreasing temperature. A theoretical model developed for explain ing the multiphonon-scattering process gives very good quantitative ag reement with the data.