In situ investigation of acetonitrile adsorption on Al2O3-coated CaF2 using sum-frequency spectroscopy

Sum-frequency spectroscopy (SFS) has been used to probe the interface between a model catalyst support (Al(2)O(3)-coated CaF(2)) and liquid consisting of neat acetonitrile and acetonitrile in ethanol. Vibrational features associated with both CN stretching ( approximately 2242 and 2281) and C-H stretching ( approximately 2942 and 2989) are observed for adsorbed nitrile. The peak positions are only slightly shifted from the bulk values, indicating weak adsorption to the model support. In the case of the neat liquid, the C-H stretching vibrations have also been probed using various polarization combinations of the sum frequency, visible and infrared beams in order to determine the orientation of the nitrile with respect to the surface. The average molecular angle calculated ( approximately 39 degrees ) shows the off-normal alignment of acetonitrile on the surface of the model support. Finally, an attempt has been made to obtain qualitative information about the adsorption isotherm of acetonitrile on Al(2)O(3)/CaF(2). The lack of curvature in the isotherm indicates the lack of affinity for the surface by acetonitrile in ethanol.