Ammonia adsorbed on Cu(110):: An angle resolved x-ray spectroscopic and ab initio study

被引:38
作者
Hasselström, J
Föhlisch, A
Karis, O
Wassdahl, N
Weinelt, M
Nilsson, A
Nyberg, M
Pettersson, LGM
Stöhr, J
机构
[1] Uppsala Univ, Dept Phys, S-75121 Uppsala, Sweden
[2] Univ Stockholm, FYSIKUM, S-11385 Stockholm, Sweden
[3] IBM Corp, Almaden Res Ctr, Div Res, San Jose, CA 95120 USA
关键词
D O I
10.1063/1.478374
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We present a study of a monolayer of ammonia (NH3) adsorbed on Cu(110) using core level spectroscopies in combination with ab initio calculations based on density functional theory. In particular, x-ray emission spectroscopy has been applied, providing an unsurpassed view of the electronic structure of NH3 upon adsorption. The saturated NH3 monolayer, Theta similar to 0.4 ML, is found to induce strong adsorbate-adsorbate interaction, causing the molecules to tilt on the surface. Based on the angular distribution of the x-ray emission (XE) spectra, we have been able to estimate a mean tilt angle from the surface normal of 40 degrees-45 degrees for the saturated monolayer; the accompanying theoretical calculations for up to three NH3 molecules on a Cu-21 all-electron cluster model support a tilted structure due to adsorbate-adsorbate dipole, and possibly hydrogen bonding, interactions. Since the creation of a core hole on the nitrogen atom site in the intermediate state of the XE process does not affect the symmetry of the molecule, a separation of valence electronic states having mainly e symmetry (N 2p(xy)) and a(1) symmetry (N 2p(z)) has been achieved using angle resolved XE measurements. In addition to the electronic states of free NH3, evidence of new, substrate induced, states has been found, interpreted as ammonia 3a(1)/4a(1)-Cu 3d valence band hybrids. It is found that back donation into the previously unoccupied ammonia 4a(1) orbital, and a simultaneous 3a(1) donation into the substrate plays an important role in the surface chemical bond. (C) 1999 American Institute of Physics. [S0021-9606(99)70610-0].
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页码:4880 / 4890
页数:11
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