INTERACTIONS IN THE COADSORPTION SYSTEM CO ACETONITRILE ON PT(111) - AN IRAS INVESTIGATION

The effect of coadsorbed acetonitrile and acetonitrile-d3 on the high (2100 cm-1) and low energg (1850 cm-1) stretching vibrational band of CO on Pt(111) has been studied at 90 K in an uhv system using ir reflection-adsorption spectroscopy (IRAS). Successive increase of the acetonitrile dosage leads to a total suppression of the strong band of preadsorbed CO at 2100 cm-1. Simultaneously the band shifts to lower frequency. At high CO precoverages a new band grows at about 2060 cm-1 (depending on precoverage). As a possible mechanism explaining the suppression we discuss the shielding of the dynamic dipole moment of the CO molecule and a change of adsorption sites induced by the coadsorbate. The adsorption site change can be monitored by observing the behaviour of the low energy band of CO at 1850 cm-1. Supposing that chemical reactions do not occur and chemical interactions are of less importance, the growth of the new band at high CO precoverages can be understood in terms of formation of CO islands with high local coverage. © 1990 Pergamon Press plc.