Co adsorbed on Cu(100): RAIRS at ultrahigh vacuum and higher pressures

Abstract

The potential of RAIRS for in-situ studies of surface species on metal single crystals under catalytic conditions is complicated by the sensitivity of such surfaces to low levels of contaminants. Using a new cell for combined UHV and higher pressure adsorption on Cu(100), the cause of previous anomalous IR spectra of CO on copper single-crystal surfaces at room temperature has been shown to be iron carbonyl. Auger spectra suggest that iron is incorporated into the copper. With purified CO the band observed at 2086 cm^–1 under UHV conditions at 120 K shows a small but significant shift to 2076 cm^–1 at 2.7 kPa and 300 K, falling to 2071 cm^–1 at 44 Pa. Under these conditions preadsorbed oxygen is reduced and produces no shift. Residues from iron carbonyl cause shifts to lower wavenumber. Preadsorbed potassium led to the appearance of bands at 2069 and 1950 cm^–1, corresponding to CO species reversibly and irreversibly adsorbed at 300 K and 1.2 kPa.