Reflection absorption infrared spectroscopy and temperature programmed desorption investigations of the interaction of methanol with a graphite surface

Abstract

Reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) have been used to investigate the adsorption of methanol (CH 3OH) on the highly oriented pyrolytic graphite (HOPG) surface. RAIRS shows that CH 3OH is physisorbed at all exposures and that crystalline CH 3OH can be formed, provided that the surface temperature and coverage are high enough. It is not possible to distinguish CH 3OH that is closely associated with the HOPG surface from CH 3OH adsorbed in multilayers using RAIRS. In contrast, TPD data show three peaks for the desorption of CH 3OH. Initial adsorption leads to the observation of a peak assigned to the desorption of a monolayer. Subsequent adsorption leads to the formation of multilayers on the surface and two TPD peaks are observed which can be assigned to the desorption of multilayer CH 3OH. The first of these shows a fractional order desorption, assigned to the presence of hydrogen bonding in the overlayer. The higher temperature multilayer desorption peak is only observed following very high exposures of CH 3OH to the surface and can be assigned to the desorption of crystalline CH 3OH. © 2005 American Institute of Physics.