PERTURBATION OF A CHEMISORBED CO MOLECULE BY PHYSISORBED XE

The interaction between physisorbed Xe and chemisorbed CO has been studied by infrared reflection absorption spectroscopy (IRAS), work function shift (DELTAphi) and temperature programmed desorption (TPD). It is found that the coadsorption of physisorbed Xe significantly affects the vibrational frequency of the CO. This is accompanied by an enhanced binding of Xe to the surface. Xe induces as much as a 55 cm-1 redshift in the CO vibrational frequency, and a 60% attenuation in the integrated CO band intensity. The redshift in CO vibrational frequency is primarily correlated with work function variations caused by coadsorbed Xe, but an additional effect due to CO layer compression caused by Xe has also been observed to produce a small blueshift. It has also been found that in Xe + CO layers, Xe exhibits a dipole moment, mu(Xe) = 0.57 D, which is independent of Xe coverage below theta(Xe) = 0.15, suggesting that Xe-Xe depolarization effects are small in the mixed layer. The interactions observed here are purely physical in character and form a basis for the interpretation of coadsorption effects which involve stronger chemical interactions added to physical effects.