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Adsorption of H2 on Ni(115): A helium diffraction study
A394 498 OXYGEN
Surface Science 173 (1986) 498-502 North-Holland, Amsterdam ISOTOPE
EXCHANGE
V.I. S O B O L E V , V . A . S O B Y A N I N , a n d G.I. P A N O V
ON Pt(100) MONOCRYSTAL A.V. PASHIS, A.V. KALINKIN
Institute of Catalysis, No~Josibirsk 630090, USSR Received 21 November 1985; accepted for publication 20 March 1986 The kinetics of homomolecular oxygen exchange on Pt(100) monocrystal has been studied over the temperature range 653-800 K and pressure range 2 100 Pa. Two regions of the reaction occurrence, which drastically differ in kinetic parameters, have been identified. In region I (high temperature, low pressure), the activation energy, E, is 185 _+20 kJ/mol and the reaction order with respect to oxygen, n, is 0_+0.1. In region II (low temperature, high pressure), E = 75_+10 kJ/mol and n = 0.6 ±0.1. The dependence of the points of reversible transition on temperature and 02 pressure when passing from one kinetic region to the other is in conformity with the diagram of the surface phase transition which has been found for oxygen adsorption on Pt(100) by Griffiths and co-workers [Surface Sci. 138 (1984) 113].
503
Surface Science 173 (1986) 503-516 North-Holland, Amsterdam CALCULATIONS
OF HELIUM
DIFFRACTION
FROM CLEAN AND H Y D R O G E N - P L A T E D
INTENSITIES
PLATINUM
Carey SCHWARTZ
Physics Division, Michelson Laboratory, Naval Weapons Center, China Lake, CA 93555. USA Received 18 October 1985; accepted for publication 28 March 1985 The scattering of helium atoms from both hydrogen-plated and clean platinum is studied theoretically by calculating the diffracted intensities. The hydrogen monolayer is modeled as either free hydrogen atoms or a layer of halves of hydrogen molecules. It is found that from the viewpoint of helium beam scattering there appears to be minimal charge transfer between the adsorbed hydrogen and the platinum substrate. It is also found that simple models of the clean platinum-helium interaction lead to poor agreement between theoretically calculated and experimental diffraction intensities. Surface Science 173 (1986) 517-537 North-Holland, Amsterdam ADSORPTION
OF
H2 ON Ni(llS): A HELIUM D I F F R A C T I O N
D o n a l d S. K A U F M A N ,
517 STUDY
L y n n R. A L L E N , E d w a r d H . C O N R A D ,
R a l p h M. A T E N a n d T h o m a s E N G E L
Department of Chemistry, University of Washington, Seattle, Washington 98195, USA Received 17 September 1985; accepted for publication 27 March 1986 The adsorption of hydrogen on Ni(ll5) has been studied. Only a (1 × 1) phase is formed where long range order is best at saturation coverage. Adsorption results in a one-dimensional surface corrugation. Using electron density contours calculated from atomic superposition, we show that the experimentally determined corrugation function is more consistent with adsorption at four-fold terrace sites than with adsorption at three-fold step sites.
Surface Science 173 (1986) 498-502 North-Holland, Amsterdam ISOTOPE
EXCHANGE
V.I. S O B O L E V , V . A . S O B Y A N I N , a n d G.I. P A N O V
ON Pt(100) MONOCRYSTAL A.V. PASHIS, A.V. KALINKIN
Institute of Catalysis, No~Josibirsk 630090, USSR Received 21 November 1985; accepted for publication 20 March 1986 The kinetics of homomolecular oxygen exchange on Pt(100) monocrystal has been studied over the temperature range 653-800 K and pressure range 2 100 Pa. Two regions of the reaction occurrence, which drastically differ in kinetic parameters, have been identified. In region I (high temperature, low pressure), the activation energy, E, is 185 _+20 kJ/mol and the reaction order with respect to oxygen, n, is 0_+0.1. In region II (low temperature, high pressure), E = 75_+10 kJ/mol and n = 0.6 ±0.1. The dependence of the points of reversible transition on temperature and 02 pressure when passing from one kinetic region to the other is in conformity with the diagram of the surface phase transition which has been found for oxygen adsorption on Pt(100) by Griffiths and co-workers [Surface Sci. 138 (1984) 113].
503
Surface Science 173 (1986) 503-516 North-Holland, Amsterdam CALCULATIONS
OF HELIUM
DIFFRACTION
FROM CLEAN AND H Y D R O G E N - P L A T E D
INTENSITIES
PLATINUM
Carey SCHWARTZ
Physics Division, Michelson Laboratory, Naval Weapons Center, China Lake, CA 93555. USA Received 18 October 1985; accepted for publication 28 March 1985 The scattering of helium atoms from both hydrogen-plated and clean platinum is studied theoretically by calculating the diffracted intensities. The hydrogen monolayer is modeled as either free hydrogen atoms or a layer of halves of hydrogen molecules. It is found that from the viewpoint of helium beam scattering there appears to be minimal charge transfer between the adsorbed hydrogen and the platinum substrate. It is also found that simple models of the clean platinum-helium interaction lead to poor agreement between theoretically calculated and experimental diffraction intensities. Surface Science 173 (1986) 517-537 North-Holland, Amsterdam ADSORPTION
OF
H2 ON Ni(llS): A HELIUM D I F F R A C T I O N
D o n a l d S. K A U F M A N ,
517 STUDY
L y n n R. A L L E N , E d w a r d H . C O N R A D ,
R a l p h M. A T E N a n d T h o m a s E N G E L
Department of Chemistry, University of Washington, Seattle, Washington 98195, USA Received 17 September 1985; accepted for publication 27 March 1986 The adsorption of hydrogen on Ni(ll5) has been studied. Only a (1 × 1) phase is formed where long range order is best at saturation coverage. Adsorption results in a one-dimensional surface corrugation. Using electron density contours calculated from atomic superposition, we show that the experimentally determined corrugation function is more consistent with adsorption at four-fold terrace sites than with adsorption at three-fold step sites.