AN INFRARED STUDY OF NO ADSORPTION AT DEFECT SITES ON PT(111)

The interaction of NO with three vicinal Pt(111) surfaces with different defect concentrations has been studied with infrared spectroscopy. The defect concentrations were calibrated using CO adsorption which has well-characterized IR bands associated with bonding at defect sites. The adsorption of NO on these platinum surfaces gives rise to numerous IR bands in the range 1320-1820 cm-1. Two of the NO bands correspond to molecules at defect sites. Molecules bound at defect sites with a linear Pt-N-O configuration yield an IR band in the range 1820-1840 cm-1 while a bent Pt-N-O species at a defect site has a wavenumber of 1609-1634 cm-1. We have directly confirmed our assignment of these bands by blocking the defect sites with atomic oxygen. Other IR bands are assigned to NO at terminal (1700-1720 cm-1) and two-fold bridge sites (1475-1500 cm-1) of the (111) terraces.