(288e) The Structure, Adsorption Isotherm, and Average Orientation of Adsorbed Alcohol Layers and Water Layers on Silicon Oxide Surfaces In Ambient Conditions

The structure, adsorption isotherm, and average orientation of adsorbed alcohol layers and water layers on clean silicon oxide surfaces in ambient conditions were studied with polarization attenuated total reflectance infrared spectroscopy (ATR-IR) as a function of partial pressure. The average orientations of the adsorbed layers were determined from the dichroic ratio of s- to p-polarization absorbances under single adsorption and co-adsorption conditions. The orientation and extent of packing were determined for linear primary alcohols ranging from propanol (C3) to octadecanol (C18) in both dry and humid environments. The molecular orientation of the adsorbed alcohol layers and dipole orientation of the adsorbed alcohol OH groups appear to be a function of partial pressure and thus isotherm thickness. Three types of vibrational peaks that correspond to liquid water, solid-like water, and ?free? OH groups respectively were observed in the adsorbed water layers on the silicon oxide surfaces in ambient conditions. The average dipole orientation of these adsorbed water layers appears to be dependent on the relative humidity. The origins of these behaviors are discussed.