Adsorption of ethyl pyruvate on Pt(111) studied by XPS and UPS

The adsorption of ethyl pyruvate on Pt(111) at low temperature was investig ated by XP and UP spectroscopy. The assignment of the photoelectron spectra was assisted by calculation of correlated ionization potentials. Compariso n of the XP and UP spectra of the condensed and chemisorbed layer indicates a strong ethyl pyruvate adsorption bond in the latter. Upon chemisorption, the HOMO of ethyl pyruvate, which is a lone-pair orbital delocalized over both C=O groups, is stabilized by about 0.7 eV with respect to the other or bitals, which is characteristic for a lone-pair bonding mechanism. The same bonding mechanism was found for coverages far below saturation. The XP spe ctra further indicate that the ketone C=O is more strongly involved in the chemisorption bond than the carboxyl C=O of ethyl pyruvate. The packing den sity of the saturated chemisorbed ethyl pyruvate layer, as determined by XP S, is high. This points toward an upright or tilted orientation of ethyl py ruvate in this layer, in line with the observed bonding mechanism.