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Theoretical study of the monolayer structures of CO adsorbed on NaCl(100)
A662 Surface Science 294 (1993) 131-140 North-Holland
Vibrational assignments for methoxy ligands on metal clusters: interpretation of RAIRS data from methoxy groups on single crystal copper surfaces Upali A. Jayasooriya, Christopher E. Anson, Osama AI-Jowder School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK
Giuseppe D'Alfonso Dipartimento di Chimica lnorganica e MetaUorganica, UniversitgJ di Milano, lrta Venezian 21, 20133 Milano, Italy
Pier Luigi Stanghellini and Rosanna Rossetti Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Material~ Universitd di Torino, I/',,, Pietro Giuria 7, 10125 Torino, Italy Received 25 February 1993; accepted for publication 25 May 1993 Vibrational frequencies of the methoxy groups in the cluster compounds [Re2(/z2-OCH3)3(CO) 6] [P(C6H5) 4] and [Re3(/~ 2H)3(kt3-OCH3XCO)9IN{P(C6H5)3}2] are assigned using selective deuterium substitution. The u~(CH3) and p(CH 3) modes were found to be the most sensitive to the state of coordination of the methoxy group. A comparison of the cluster data with P,J d R S data for methanol adsorbed on Cu(100) and C u ( l l l ) single crystal faces provides a unif36ng model for the surface m e ~ species. This consists of/z2-coordinated methoxy groups tilted to the surface normal on both surfaces at low coverage, but with the tilt angle decreasing with higher surface coverage.
Surface Science 294 (1993) 141-148 North-Holland
Capture and deso~tion processes in the elastic scattering of atoms by stepped surfaces S. Miret-Art~s lnstituto de Matemdticas y F(sica Fundamenta~ CSIC, Serrano 123, 28006 Madrid, Spain Received 4 January 1993; accepted for publication 24 May 1993 In this paper, we show that, for stepped surfaces, dynamics is not time reversal invariant and important consequences can be derived from this fact. Thus, and being guided by arguments similarly used in nuclear scattering, we can define elastic capture or sticking probabilities and cross sections. These probabilities can display the critical kinematic effect where in a very broad energetic region they present a very typical structure. At the same time, depending on the scattering type involved, downstairs or upstairs, these probabilities and their corresponding profiles are different as well as the elastic desorption probabilities into the different open diffraction channels. Surface Science 294 (1993) 149-160 North-Holland
Theoretical study of the monolayer structures of CO adsorbed on NaCl(100) S. Pieaud, P.N.M. Hoang, C. Girardet Laboratoire de Physique Mol~ulaire URA CNRS 772, Universit~ de Franche Comte, 25030 Besan~on Cedex, France
A. Meredith and A.J. Stone University Chemical Laboratory, L e ~
Road, Cambridge CB2 1EW, UK
A663 Received 22 March 1993; accepted for publication 9 June 1993 Interaction potential calculations are performed to interpret recent experimental results on the geometry of CO monolayers adsorbed on clean NaCI(100) substrate deduced from polarized Fourier transform infrared spectroscopy and helium beam scattering. Two isoenergetical structures are calculated: the (1 × 1) geometry with the molecular axes standing upright or inclined with respect to the surface normal and the (2 × 1) geometry with the molecular axes inclined and tilted anti-parallel. A statistical analysis of the energy minima for the CO monolayer is performed and it is shown that the transition from the (2 × 1) to the (1 × 1) structure can proceed in a very small energy range ( ~ a few meV) leading to a rearrangement of the molecular canters of mass above the Na sites with a concomitant redistribution of the molecular axis orientations. These results are in close agreement with experiments indicating a phase transition at 35 K from the (2 × 1) to the (1 × 1) phase.
Surface Science 294 (1993) 161-183 North-Holland
Theory of electron emission stimulated by charged particle reflection from simple metals; glancing incidence D.L. Mills Department of Physics, University of California, Irvine, CA 92717, USA Received 29 December 1992; accepted for publication 6 May 1993 Recent experiments by Rau and his colleagues [Phys. Rev. Lett. 64 (1990) 1441; DIET V (Springer, New York, 1992); Ionization of Solids by Heavy Particles (Plenum, New York, 1992)] explore the energy spectrum of electrons emitted from metal surfaces, in response to the reflection of positive ions reflected from the surface, at grazing incidence. We develop a theory of the emission process wherein the Coulomb field of the ion excites particle-hole pairs in the substrate, taken here to be jellium. We obtain a general expression for the energy and angle variation of the emitted electrons, for an ion trajectory which may penetrate into the substrate before reflecting off the planes of substrate nuclei. The result is expressed as an integral over the density-density response functions X(zz'; QII¢O)of the substrate. Special limits are explored, with emphasis on glancing incidence. We do not consider Auger processes, in which the ion is neutralized through acquisition of a substrate electron.
Surface Science 294 (1993) 185-196 North-Holland
Surface diffusion of potassium on Ru(OO1) E.D. Westre, D.E. Brown, J. Kutzner 1 and S.M. George Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA Received 24 February 1993; accepted for publication 19 May 1993 The surface diffusion of potassium on Ru(081) was studied using laser-induced thermal desorption (LITD) techniques. The potassium surface mobifity was very dependent on the potassium surface coverage. The coverage dependent surface diffusion coefficients were obtained from an iterative analysis based on surface diffusion measurements performed at different initial coverages. At 220 K, the surface diffusion coefficient increased dramatically as the potassium coverage increased from 0 K = 0.08 to 0.33 ML. The surface diffusion coefficients also displayed Arrbenius behavior at various temperatures and potassium coverages. As the potassium coverage increased from 0 K = 0.15 to 0.33 ML, the surface diffusion activation energy decreased slightly and the diffusion pre-exponential increased by a factor of 35. The diffusion activation energies were Edit = 9.0 + 0.4, 8.5 + 0.3 and 8.1 + 0.4 kcal/mol and the corresponding pre-exponentials were D o = 0.40 + 0.06, 4.4 + 0.3 and 14.0 + 0.5 cm2/s at 0g = 0.15, 0.25 and 0.33 ML, respectively. The coverage dependence of the potassium surface diffusion on Ru(001) was attn3mted to strong repulsive interactions between potassium adatoms. These interactions most likely originate from repulsions between dipoles formed by partially ionized potassium adatoms and their surface image charges.
Vibrational assignments for methoxy ligands on metal clusters: interpretation of RAIRS data from methoxy groups on single crystal copper surfaces Upali A. Jayasooriya, Christopher E. Anson, Osama AI-Jowder School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK
Giuseppe D'Alfonso Dipartimento di Chimica lnorganica e MetaUorganica, UniversitgJ di Milano, lrta Venezian 21, 20133 Milano, Italy
Pier Luigi Stanghellini and Rosanna Rossetti Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Material~ Universitd di Torino, I/',,, Pietro Giuria 7, 10125 Torino, Italy Received 25 February 1993; accepted for publication 25 May 1993 Vibrational frequencies of the methoxy groups in the cluster compounds [Re2(/z2-OCH3)3(CO) 6] [P(C6H5) 4] and [Re3(/~ 2H)3(kt3-OCH3XCO)9IN{P(C6H5)3}2] are assigned using selective deuterium substitution. The u~(CH3) and p(CH 3) modes were found to be the most sensitive to the state of coordination of the methoxy group. A comparison of the cluster data with P,J d R S data for methanol adsorbed on Cu(100) and C u ( l l l ) single crystal faces provides a unif36ng model for the surface m e ~ species. This consists of/z2-coordinated methoxy groups tilted to the surface normal on both surfaces at low coverage, but with the tilt angle decreasing with higher surface coverage.
Surface Science 294 (1993) 141-148 North-Holland
Capture and deso~tion processes in the elastic scattering of atoms by stepped surfaces S. Miret-Art~s lnstituto de Matemdticas y F(sica Fundamenta~ CSIC, Serrano 123, 28006 Madrid, Spain Received 4 January 1993; accepted for publication 24 May 1993 In this paper, we show that, for stepped surfaces, dynamics is not time reversal invariant and important consequences can be derived from this fact. Thus, and being guided by arguments similarly used in nuclear scattering, we can define elastic capture or sticking probabilities and cross sections. These probabilities can display the critical kinematic effect where in a very broad energetic region they present a very typical structure. At the same time, depending on the scattering type involved, downstairs or upstairs, these probabilities and their corresponding profiles are different as well as the elastic desorption probabilities into the different open diffraction channels. Surface Science 294 (1993) 149-160 North-Holland
Theoretical study of the monolayer structures of CO adsorbed on NaCl(100) S. Pieaud, P.N.M. Hoang, C. Girardet Laboratoire de Physique Mol~ulaire URA CNRS 772, Universit~ de Franche Comte, 25030 Besan~on Cedex, France
A. Meredith and A.J. Stone University Chemical Laboratory, L e ~
Road, Cambridge CB2 1EW, UK
A663 Received 22 March 1993; accepted for publication 9 June 1993 Interaction potential calculations are performed to interpret recent experimental results on the geometry of CO monolayers adsorbed on clean NaCI(100) substrate deduced from polarized Fourier transform infrared spectroscopy and helium beam scattering. Two isoenergetical structures are calculated: the (1 × 1) geometry with the molecular axes standing upright or inclined with respect to the surface normal and the (2 × 1) geometry with the molecular axes inclined and tilted anti-parallel. A statistical analysis of the energy minima for the CO monolayer is performed and it is shown that the transition from the (2 × 1) to the (1 × 1) structure can proceed in a very small energy range ( ~ a few meV) leading to a rearrangement of the molecular canters of mass above the Na sites with a concomitant redistribution of the molecular axis orientations. These results are in close agreement with experiments indicating a phase transition at 35 K from the (2 × 1) to the (1 × 1) phase.
Surface Science 294 (1993) 161-183 North-Holland
Theory of electron emission stimulated by charged particle reflection from simple metals; glancing incidence D.L. Mills Department of Physics, University of California, Irvine, CA 92717, USA Received 29 December 1992; accepted for publication 6 May 1993 Recent experiments by Rau and his colleagues [Phys. Rev. Lett. 64 (1990) 1441; DIET V (Springer, New York, 1992); Ionization of Solids by Heavy Particles (Plenum, New York, 1992)] explore the energy spectrum of electrons emitted from metal surfaces, in response to the reflection of positive ions reflected from the surface, at grazing incidence. We develop a theory of the emission process wherein the Coulomb field of the ion excites particle-hole pairs in the substrate, taken here to be jellium. We obtain a general expression for the energy and angle variation of the emitted electrons, for an ion trajectory which may penetrate into the substrate before reflecting off the planes of substrate nuclei. The result is expressed as an integral over the density-density response functions X(zz'; QII¢O)of the substrate. Special limits are explored, with emphasis on glancing incidence. We do not consider Auger processes, in which the ion is neutralized through acquisition of a substrate electron.
Surface Science 294 (1993) 185-196 North-Holland
Surface diffusion of potassium on Ru(OO1) E.D. Westre, D.E. Brown, J. Kutzner 1 and S.M. George Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA Received 24 February 1993; accepted for publication 19 May 1993 The surface diffusion of potassium on Ru(081) was studied using laser-induced thermal desorption (LITD) techniques. The potassium surface mobifity was very dependent on the potassium surface coverage. The coverage dependent surface diffusion coefficients were obtained from an iterative analysis based on surface diffusion measurements performed at different initial coverages. At 220 K, the surface diffusion coefficient increased dramatically as the potassium coverage increased from 0 K = 0.08 to 0.33 ML. The surface diffusion coefficients also displayed Arrbenius behavior at various temperatures and potassium coverages. As the potassium coverage increased from 0 K = 0.15 to 0.33 ML, the surface diffusion activation energy decreased slightly and the diffusion pre-exponential increased by a factor of 35. The diffusion activation energies were Edit = 9.0 + 0.4, 8.5 + 0.3 and 8.1 + 0.4 kcal/mol and the corresponding pre-exponentials were D o = 0.40 + 0.06, 4.4 + 0.3 and 14.0 + 0.5 cm2/s at 0g = 0.15, 0.25 and 0.33 ML, respectively. The coverage dependence of the potassium surface diffusion on Ru(001) was attn3mted to strong repulsive interactions between potassium adatoms. These interactions most likely originate from repulsions between dipoles formed by partially ionized potassium adatoms and their surface image charges.