(97i) Investigation of Acetonitrile Adsorption on a Model Support by Method of Sum Frequency Spectroscopy

Sum-Frequency spectroscopy (SFS) is a relatively new technique used for investigating ?buried interfaces.? SFS is a non-linear approach, which enables it to selectively probe interfacial molecular vibrational properties, even in the presence of significant bulk phase species with similar or identical vibrational signatures. In this study, SFS has been used to probe the interface between a model support of Al2O3 and liquid mixtures consisting of acetonitrile in ethanol. Vibrational features associated with both C≡N stretching (ca 2250 cm-1) and C-H stretching (2800-3000 cm-1) are observed for adsorbed acetonitrile. The study of nitrile adsorption at different acetonitrile concentrations in ethanol was used to form an adsorption isotherm wherein this isotherm will be used in future nitrile hydrogenation studies. In addition, the C-H stretching vibrations have also been probed using various polarizations combinations of the sum frequency, visible and infrared beams in order to determine the orientation of acetonitrile with respect to the surface normal. However due to the birefringence of the Al2O3 support, the orientation studies were inconclusive.