DIRECT OBSERVATION OF THE MOLECULAR INTERACTION BETWEEN CHEMISORBED CO AND WATER OVERLAYER ON PT(111)

The behavior of CO on Pt(111) co-adsorbed with water is interpreted fr om the adsorbed CO-water and the Pt substrate-water interactions. On t he surface with CO coverage of 0.5 ML (theta(co)=0.5 ML), owing to the direct interaction between the adsorbed CO and water, the vibrational frequency of the CO stretching mode (GO) shows a red shift accompanie d by the appearance of a newly observed vibrational mode of water mole cules at 2680 cm(-1). For the theta(co)=0.05 ML surface, the occupatio n of the on-top site of Pt(111) by a water molecule induces a large re d shift in CO to 1803 by substrate-mediated interaction. Upon annealin g, a further red shift in CO to 1704 cm(-1) is also observed. (C) 1997 Elsevier Science B.V.