VOLUME 44, NUMBER 10 PHYSICAL REVIEW LETTERS 10 MARCH 1980 A. J. Greenfield, J. Phys. (Paris), Colloq. 39, C6-496 (1978), and subsequently withdrawn in Ref. 1. R. M. Boysel, R. S. Newrock, and J. C. Garland, J. Phys. F 9, L191 (1979), have already elucidated their source. ~L. Q. Aslamazov and A. I. Larkin, Fiz. Tverd. Tela. 10, 1104 (1968) [Sov. Phys. Solid State 10, 875 (1968)]; K. Maki, Prog. Theor. Phys. 40, 875 (1968); R. S. Thompson, Phys. Rev. B 1, 327 (1970); P. G. Hohen- berg, in Proceedings of the Twelfth International Con ference on Low TemPerature Physics, Kyoto, 2970, edited by E, Kanda (Keigaku Publishing Co. Ltd. , Tokyo, 1971), p. 211. B. R. Barnard, Ph. D. thesis, University of London, 1979 {unpublished) . 'B. R. Barnard and A. D. Caplin, J. Phys. E 11, 1117 (1978) . 6F. A. Shunk, Constitution of Binary Alloys (McGraw- Hill, New York, 1969), 2nd suppl. , p. 27. VJ. C. Garland and D. J. van Harlingen, J. Phys. F 8, 117 (1978) . H. van Kempen, J. H. J. M. Ribot, and P. V?yder, J. Phys. (Paris), Colloq. 39, C6-1048 (1978); J. H. J. M. Ribot, J. Bass, H. van Kempen, and P. ryder, J. Phys. F 9, L117 (1979); J. H. J. M. Ribot, J. Bass, H. van Kempen, and P. ryder, to be published. T. Claeson and J. Ivarsson, Commun. Phys. 2, 53 (1977). ' M. F. Merriam and M. van Herzen, Phys. Rev. 131, 637 (1963); J. Blanc, A. ¹moz, and J. C. Solecki, in Proceedings of the Twelfth International Conference on Jo~ TemPerature Physics, Kyoto, 1970, edited by E. Kanda (Keigaku Publishing Co. Ltd. , Tokyo, 1971), p. 297. '1F. R. Gamble and H. M. McConnell, Phys. Lett. 26A, 162 (1968). "W. C. H. Joiner, Phys. Rev. 137, A112 (1965). ' W. H. Keesom, Kamerlingh Onnes Laboratory, Leiden, Communication No. 224C, 1933 (unpublished). '4D. L. Edmunds, W. P. Pratt, Jr. , and J. A. How- lands, to be published. Identification of an Adsorbed Hydroxyl Species on the Pt(111) Surface Galen B. Fisher and Brett A. Sexton I'hysical Chemistry Department, General Motors Research Laboratories, ~arren, Michigan 48090 (Received 26 November 1979) The electronic structure and vibrations of an adsorbed hydroxyl (OH) species are ident- ified and characterized for the first time on a transition-metal surface. In this study of water's interaction with clean Pt(ill) in ultrahigh vacuum, water adsorbed at 100 K de- sorbs at 180 K without appreciable dissociation. However, in the presence of adsorbed atomic oxygen, water dissociates above 150 K to form adsorbed hydroxyl species. The O-H axis appears to be bent relative to the surface normal. %e reprot in this Letter the first evidence, supported by a combination of spectroscopies, for the existence of an adsorbed hydroxyl species on a single-crystal transition-metal surface. This finding has particular significance, since the direct observation of intermediate steps in catalytic reactions has proven very difficult even with many advances in our understanding of ad- sorbed atoms and molecules from a number of spectroscopies. Despite consideration study since the time of Faraday, ' even the simplest oxidation reaction, that of hydrogen oxidation over Pt to form water (2H, +0, -2H, O), has not had its mechanism elucidated over its entire tem- perature range. A wide range of mechanisms has been discussed for this reaction, including the reaction of adsorbed hydroxyl species with adsorbed hydrogen to form water. ' However, at room temperature and above where the research is usually done, the reaction has more recently been discussed as a Langmuir-Hinshelwood proc- ess, in which an adsorbed dihydrogen species reacts with adsorbed oxygen to form water which then desor'bs. ' As part of a study of this reaction in ultrahigh vacuum over single-crystal Pt(111), we have identified and characterized for the first time the electronic structure and vibrations of an adsorbed hydroxyl or OH species by means of ultraviolet photoemission spectroscopy (UPS), x-ray photoemission spectroscopy (XPS), and high-resolution (65 cm ' or 8 meV) electron en- ergy loss spect-roscopy (EELS). The hydroxyl appears to exist at temperatures which relate to the water formation reaction. During a study of water desorption from' Pt(111) it was found that water's desorption behavior is quite different from clean Pt(ill) than from a sur- face with oxygen present. Figure 1 shows the rate of water desorption from Pt(111) after a con- stant exposure of 0.3 L (coverage less than a monolayer) to surfaces which are clean and pre- exposed to small amounts of oxygen (1 L = 1 lang- 1980 The American Physical Society 683