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Symmetry, orientation and surface chemistry of aromatic molecules on transition metal surfaces
Journal of Molecular Catalysis, 51 (1989)
369 - 370
369
SYMMETRY, ORIENTATION AND SURFACE CHEMISTRY OF AROMATIC MOLECULES ON TRANSITION METAL SURFACES FALKO P. NETZER Znstitut fiir Physikalische Chemie, Uniuersitiit Innsbruck,
A-6020 Innsbruck
(Austria)
Extended Abstract
The structure and orientation of aromatic molecules on transition metal single crystal surfaces has been determined from angle-resolved UV photoelectron spectroscopy (ARUPS) data, which were obtained with the use of synchrotron radiation; complementary information has been provided by low energy electron diffraction (LEED), thermal desorpti,on mass spectrometry (TDS) and measurements of the work function. The symmetry of an adsorption complex can be determined in ARUPS via polarisation-dependent selection rules, and from the symmetry of the surface molecule the orientation with respect to the surface plane and the surface chemical bond can be specified. The symmetry analysis of molecular ARUPS is first discussed, and then, these principles are applied to the benzene/Rh(lll) [l, 21 and benzene/Pd( 110) [ 31 systems. In these two adsorption systems, well-ordered adsorbate overlayer structures are observed, and the ARUPS analysis yields a detailed picture of the adsorbate structure. Second, the surface chemistry of five-membered ring systems on Rh(ll1) is elucidated. Desulfurisation of thiophene at low temperatures is investigated [ 41, and the spectroscopic identification of adsorbed cyclopentadienyl CSH, species, formed by dehydrogenation of cyclopentene and cyclopentadiene on Rh(lll), is reported [5,6]. It was found that thiophene is adsorbed in a monolayer with the ring plane parallel to the surface, and that the desulfurisation reaction is initiated at T 2 150 K. After desulfurisation, a C4 hydrocarbon residue is left at the Rh(ll1) surface, which can be are desorbed partly as butadiene. Cyclopentene and cyclopentadiene n-bonded in the low temperature monolayer, and cyclopentadiene dehydrogenates to C,H, at T > 150 K. In contrast, CSH, is only formed from cyclopentene after room temperature adsorption. Annealing of a cyclopentene monolayer at T > 190 K yi.elds different surface species, of C&H, stoichiometry, which are interpreted tentatively as q4 (tetra-sigma bonded) cyclopentane. References 1 M. Neumann, J. U. Mack, E. Bertel and F. P. Netzer, Surf. Sci., 155 (1985) 629. 2 F. P. Netzer, G. Rosina, E. Bertel and H. Saalfeld, Surf. Sci., 184 (1987) L397. 0304-5102/89/$3.50
0 Elsevier Sequoia/Printed in The Netherlands
370 3 F. P. Netzer, G. Rangelov, G. Rosina, H. B. Saalfeld, M. Neumann and D. R. Lloyd, Phys. Rev. B, 37 (1988) 10399. 4 F. P. Netzer, E. Bertel and A. Goldmann, Surf. Sci., 201 (1988) 257. 5 F. P. Netzer, A. Goldmann, G. Rosina and E. Bertel, Surf. Sci., 204 (1988) 387. 6 F. P. Netzer, G. Rosina, E. Bertel and H. B. Saalfeld, J. Electron Spectrosc. Relut. Phenom., 46 (1988) 373.
369 - 370
369
SYMMETRY, ORIENTATION AND SURFACE CHEMISTRY OF AROMATIC MOLECULES ON TRANSITION METAL SURFACES FALKO P. NETZER Znstitut fiir Physikalische Chemie, Uniuersitiit Innsbruck,
A-6020 Innsbruck
(Austria)
Extended Abstract
The structure and orientation of aromatic molecules on transition metal single crystal surfaces has been determined from angle-resolved UV photoelectron spectroscopy (ARUPS) data, which were obtained with the use of synchrotron radiation; complementary information has been provided by low energy electron diffraction (LEED), thermal desorpti,on mass spectrometry (TDS) and measurements of the work function. The symmetry of an adsorption complex can be determined in ARUPS via polarisation-dependent selection rules, and from the symmetry of the surface molecule the orientation with respect to the surface plane and the surface chemical bond can be specified. The symmetry analysis of molecular ARUPS is first discussed, and then, these principles are applied to the benzene/Rh(lll) [l, 21 and benzene/Pd( 110) [ 31 systems. In these two adsorption systems, well-ordered adsorbate overlayer structures are observed, and the ARUPS analysis yields a detailed picture of the adsorbate structure. Second, the surface chemistry of five-membered ring systems on Rh(ll1) is elucidated. Desulfurisation of thiophene at low temperatures is investigated [ 41, and the spectroscopic identification of adsorbed cyclopentadienyl CSH, species, formed by dehydrogenation of cyclopentene and cyclopentadiene on Rh(lll), is reported [5,6]. It was found that thiophene is adsorbed in a monolayer with the ring plane parallel to the surface, and that the desulfurisation reaction is initiated at T 2 150 K. After desulfurisation, a C4 hydrocarbon residue is left at the Rh(ll1) surface, which can be are desorbed partly as butadiene. Cyclopentene and cyclopentadiene n-bonded in the low temperature monolayer, and cyclopentadiene dehydrogenates to C,H, at T > 150 K. In contrast, CSH, is only formed from cyclopentene after room temperature adsorption. Annealing of a cyclopentene monolayer at T > 190 K yi.elds different surface species, of C&H, stoichiometry, which are interpreted tentatively as q4 (tetra-sigma bonded) cyclopentane. References 1 M. Neumann, J. U. Mack, E. Bertel and F. P. Netzer, Surf. Sci., 155 (1985) 629. 2 F. P. Netzer, G. Rosina, E. Bertel and H. Saalfeld, Surf. Sci., 184 (1987) L397. 0304-5102/89/$3.50
0 Elsevier Sequoia/Printed in The Netherlands
370 3 F. P. Netzer, G. Rangelov, G. Rosina, H. B. Saalfeld, M. Neumann and D. R. Lloyd, Phys. Rev. B, 37 (1988) 10399. 4 F. P. Netzer, E. Bertel and A. Goldmann, Surf. Sci., 201 (1988) 257. 5 F. P. Netzer, A. Goldmann, G. Rosina and E. Bertel, Surf. Sci., 204 (1988) 387. 6 F. P. Netzer, G. Rosina, E. Bertel and H. B. Saalfeld, J. Electron Spectrosc. Relut. Phenom., 46 (1988) 373.