FUNDAMENTAL, OVERTONE AND COMBINATION VIBRATIONS IN CONDENSED METHANOL STUDIED WITH LOW-ENERGY ELECTRON-ENERGY-LOSS SPECTROSCOPY

High-resolution electron-energy-loss spectroscopy, within the incident electron energy range 1 to 20 eV, was performed for solid methanol co ndensed at 15 K on a polycrystalline platinum substrate. Besides the m ost prominent energy loss peaks, which correspond to the fundamental v ibrations, we observe several medium and small energy loss features th at are ascribed to overtone and combination bands of some fundamentals . The effects of the film thickness and electron impact energy are sho wn for the fundamental as well as for the overtone and combination vib rations. The incident energy at which resonance enhancement occurs for the fundamentals favors the observation of the non-fundamental modes within and beyond the normal infrared frequency range. The first overt one of the CO stretching mode is found at 255 meV. The combination of the CH3 rocking vibration with the OH in-plane bending or the CH3 asym metric bending mode is located at 320 meV. The series of additional en ergy loss bands, appearing beyond the normal infrared region ( < 450 m eV), are assigned to several vibrational progressions, most of which h ave their origin at the CH3 asymmetric stretching modes at 368 meV. (C ) 1998 Elsevier Science B.V. All rights reserved.