No adsorption on Pt(111)

The interaction of NO with a Pt(111) surface was studied by means of XPS, LEED and AES at 120 K and 305 K. The observed changes in the valence and O(1s) and N(1s) core level spectra during NO adsorption and stepwise heating of the adsorbed layer as well as the estimated O : N atomic ratios supported molecular NO adsorption on Pt(111). The NO saturation coverage was found to increase from 0.23 at 305 K to 0.54 at 120 K. At both adsorption temperatures and at coverages less than 0.15 only a single adsorption state was populated characterized by an O(1s) binding energy of 530.6 eV and a dipole moment of 0.42 D, negative end outwards. At higher coverages, a second state characterized by an O(1s) binding energy of 532.5 eV appeared. These two states are associated with bridge and linearly bonded NO, respectively, in accordance with existing vibrational data. For high NO coverages achieved after adsorption at 120 K the XPS O(1s) spectra produce evidence of an adsorbed NO species characterized by an O(1s) binding energy of ~ 531.1 eV. This species may correspond to disordered NO molecules unobservable by infra-red spectroscopy.