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Ethylidyne on Pt(111): determination of adsorption site, substrate relaxation and coverage by automated tensor LEED
A335 Surface Science 286 (1993) 1-14 North-Holland
Ethylidyne on P t ( l l l ) : determination of adsorption site, substrate relaxation and coverage by automated tensor LEED U. Starke, A. Barbieri, N. Materer, M.A. Van Hove and G.A. Somorjai Materials Sciences Division, Lawrence Berkeley Laboratory and Department of Chemistry, Uniuersity of California, Berkeley, CA 94720, USA Received 2 November 1992; accepted for publication 30 November 1992 The adsorption of ethylidyne on P t ( l l l ) is investigated by low-energy electron diffraction (LEED). An automated search program for L E E D structure analysis is used to determine the adsorption geometry from comparison of experiment and theory. The fcc threefold hollow site is preferred by the fit. The c a r b o n - c a r b o n bond distance is 1.49 A and the c a r b o n - p l a t i n u m bond length 1.9l A. A buckling within the top two substrate layers is detected which corresponds to a local expansion of the first-to-second layer distance u n d e r n e a t h the adsorbate by 0.08 ,~ as compared to the bulk value. The three substrate atoms forming the hollow site are closer to one another than in the bulk structure by 0.11 A. A tilt of the c a r b o n - c a r b o n bond by 6 ° seems to occur and could be indicative of a wagging vibration of this bond. The hydrogen atoms do not contribute to the diffraction that yields the ordered pattern as indicated by the absence of hydrogen related features in the experimental I - V curves, suggesting relatively free rotation of the methyl group about the c a r b o n - c a r b o n axis. Additionally, a distinction between a p(2 × 2) and an average of three domains of a p(2 x 1) structure, which both give rise to the same (2 x 2) L E E D pattern, is possible. The p(2 x 2) is favored in the structural analysis, giving an ethylidyne coverage of 0.25 monolayers.
Surface Science 286 (1993) 15-25 North-Holland
The interpretation of CO adsorbed on P t / S i O 2 of two different particle-size distributions Robert K. Brandt, M.R. Hughes 1, L.P. Bourget 2, K. Truszkowska 3 and Robert G. Greenler * Department of Physics and Laboratory for Surface Studies, University of Wisconsin-Milwaukee, Milwaukee. WI 53201, USA Received 30 July 1992; accepted for publication 16 D e c e m b e r 1992 The infrared transmission spectra have been obtained for CO adsorbed o n silica-supported platinum particles with two different particle-size distributions. The smaller has a m e a n m e a s u r e d diameter of 11 A; the larger, 39 A. The spectra have been interpreted by comparison with calculated spectra from CO adsorption on model particles. The differences in the infrared spectra for the different particle sizes are attributed to the relative n u m b e r of surface atoms in the Pt particles with different coordination numbers.
Surface Science 286 (1993) 26-45 North-Holland
On the coadsorption of CO and alkali atoms at transition metal surfaces: a LCGTO-LDF cluster study A. G6rling, L. Ackermann, J. Lauber, P. Knappe and N. R6sch * Lehrstuhl ]~ir Theoretische Chemie, Technische Universitiit Miinchen, D-8046 Garching, Germany Received 24 November 1992; accepted for publication 20 January 1993
Ethylidyne on P t ( l l l ) : determination of adsorption site, substrate relaxation and coverage by automated tensor LEED U. Starke, A. Barbieri, N. Materer, M.A. Van Hove and G.A. Somorjai Materials Sciences Division, Lawrence Berkeley Laboratory and Department of Chemistry, Uniuersity of California, Berkeley, CA 94720, USA Received 2 November 1992; accepted for publication 30 November 1992 The adsorption of ethylidyne on P t ( l l l ) is investigated by low-energy electron diffraction (LEED). An automated search program for L E E D structure analysis is used to determine the adsorption geometry from comparison of experiment and theory. The fcc threefold hollow site is preferred by the fit. The c a r b o n - c a r b o n bond distance is 1.49 A and the c a r b o n - p l a t i n u m bond length 1.9l A. A buckling within the top two substrate layers is detected which corresponds to a local expansion of the first-to-second layer distance u n d e r n e a t h the adsorbate by 0.08 ,~ as compared to the bulk value. The three substrate atoms forming the hollow site are closer to one another than in the bulk structure by 0.11 A. A tilt of the c a r b o n - c a r b o n bond by 6 ° seems to occur and could be indicative of a wagging vibration of this bond. The hydrogen atoms do not contribute to the diffraction that yields the ordered pattern as indicated by the absence of hydrogen related features in the experimental I - V curves, suggesting relatively free rotation of the methyl group about the c a r b o n - c a r b o n axis. Additionally, a distinction between a p(2 × 2) and an average of three domains of a p(2 x 1) structure, which both give rise to the same (2 x 2) L E E D pattern, is possible. The p(2 x 2) is favored in the structural analysis, giving an ethylidyne coverage of 0.25 monolayers.
Surface Science 286 (1993) 15-25 North-Holland
The interpretation of CO adsorbed on P t / S i O 2 of two different particle-size distributions Robert K. Brandt, M.R. Hughes 1, L.P. Bourget 2, K. Truszkowska 3 and Robert G. Greenler * Department of Physics and Laboratory for Surface Studies, University of Wisconsin-Milwaukee, Milwaukee. WI 53201, USA Received 30 July 1992; accepted for publication 16 D e c e m b e r 1992 The infrared transmission spectra have been obtained for CO adsorbed o n silica-supported platinum particles with two different particle-size distributions. The smaller has a m e a n m e a s u r e d diameter of 11 A; the larger, 39 A. The spectra have been interpreted by comparison with calculated spectra from CO adsorption on model particles. The differences in the infrared spectra for the different particle sizes are attributed to the relative n u m b e r of surface atoms in the Pt particles with different coordination numbers.
Surface Science 286 (1993) 26-45 North-Holland
On the coadsorption of CO and alkali atoms at transition metal surfaces: a LCGTO-LDF cluster study A. G6rling, L. Ackermann, J. Lauber, P. Knappe and N. R6sch * Lehrstuhl ]~ir Theoretische Chemie, Technische Universitiit Miinchen, D-8046 Garching, Germany Received 24 November 1992; accepted for publication 20 January 1993