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 from the adsorbed CO-water and the Pt substrate-water interactions. On the 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 accompanied by the appearance of a newly observed vibrational mode of water molecules at 2680 cm(-1). For the theta(co)=0.05 ML surface, the occupation of the on-top site of Pt(111) by a water molecule induces a large red shift in CO to 1803 by substrate-mediated interaction. Upon annealing, a further red shift in CO to 1704 cm(-1) is also observed. (C) 1997 Elsevier Science B.V.