A high resolution vibrational spectroscopic study of CO/K coadsorption on Pt{111}

The coadsorption of potassium and CO on Pt{111} has been investigated with infrared reflection-absorption spectroscopy (IRAS) and LEED by varying the individual coverages of both species over a wide range. The vibrational data show several C-O stretching bands with frequencies between 1390 and 1802 cm-1 each of which consists of several absorption lines: up to a K coverage of θK = 0.2 additional vibrational frequencies were detected between 1830 and 2105 cm-1 which differ only slightly from those on the K-free surface. Five different ordered overlayers could be distinguished. The combination of IRAS and LEED results indicate that the favoured CO bonding site changes from on-top to bridge, in accordance with the results of recent calculations. The site change is confined to the immediate surrounding of the K atoms. The results can be explained by a dominant attractive short-range interaction between CO and K but also show the existence of a weaker long-range interaction. © 1993.