WATER-ADSORPTION ON PT(111) - FROM ISOLATED MOLECULE TO 3-DIMENSIONAL CLUSTER

Water adsorption on Pt(111) at 84 K was investigated by infrared reflection absorption spectroscopy. At a low coverage (theta=0.13 ML), D2O adsorption exhibited absorption bands of v(OD) at 2475 cm(-1) and delta(D2O) at 1.184 cm(-1). The species is assigned to isolated D2O bound to the surface through the oxygen lone-pair. With increasing coverage (0.13<theta<0.67 ML), a strong lateral interaction through hydrogen bonding induces the clustering of water molecules showing an additional absorption of v(OD) around 2550 cm(-1) and an enhancement in the intensity of delta(D2O). Further exposure yields ice growth and also causes a longitudinal interaction between chemisorbed water adjacent to the surface and ice overlayers. Isolated water decreases its fractional coverage because it is included into the hydrogen bonding network of ice overlayers.