DIRECT STRUCTURE DETERMINATION OF OXYGEN ADSORBED ON SILVER BY REFLECTION-ABSORPTION INFRARED-SPECTROSCOPY WITH ISOTOPIC-SUBSTITUTION

Reflection-absorption infrared spectroscopy (RAIRS) in the spectral region 1700-280 cm-1 is used to identify and characterize three forms of oxygen adsorbed on a polycrystalline silver ribbon. The high resolution of RAIRS allows us to interpret the spectra resulting from adsorption of mixed oxygen isotopes to identify directly two molecular forms and atomic form of adsorbed oxygen, and to determine the adsorption geometry of the two molecular forms. One of the molecular forms, existing at temperatures below 265 K, is standing up on the surface and has an O-O stretching frequency of 983 cm-1. The Ag-O stretching frequency for this species is predicted to be 210 cm-1. Another molecular form, existing at temperatures below 185 K, lies parallel to the surface with an O-O stretching vibration at 622 cm-1. A third form, the atomic oxygen, is produced by adsorption between 300 and 560 K, and has an Ag-O stretching vibration at 351 cm-1.