Kinetics and dynamics in physisorption of CH3Cl on HOPG: surface temperature and molecular orientation dependence

Abstract

We report a study of kinetics and dynamics in physisorption of CH₃Cl on a highly-oriented pyrolytic graphite (HOPG). Thermal energy atom scattering (TEAS) was used to probe the kinetics of thermal CH₃Cl adsorption on HOPG during the coverage evolution. The desorption energy of CH₃Cl on HOPG changes from 0.25 to 0.30 eV with increasing surface coverage, suggesting the attractive interaction between CH₃Cl molecules on the surface. On the other hand, the oriented molecular beam scattering was used to monitor the dynamical interaction of CH₃Cl with HOPG at zero coverage, demonstrating that the CH₃Cl scattering intensity depends on the molecular orientation of the incident CH₃Cl. The observed steric preference is not sensitive to the surface temperature. These results suggest that the moderate anisotropy in the interaction potential induces the molecular-orientation dependence of energy dissipation during the transient trapping into the physisorption well.