Oström H, Ogasawara H, Näslund L-A, Andersson K, Pettersson L G M, Nilsson A
Stockholm University, Fysikum, SE-106 91 Stockholm, Sweden.
J Chem Phys. 2007 Oct 14;127(14):144702. doi: 10.1063/1.2781470.
The electronic structure of methane adsorbed on Pt(977) is investigated using angle-resolved x-ray absorption spectroscopy (XAS) in combination with density functional theory spectrum calculations. XAS, which probes the unoccupied states atom specifically, shows the appearance of the symmetry-forbidden gas-phase lowest unoccupied molecular orbital due to s-p rehybridization. In addition new adsorption-induced states appear just above the Fermi level. A systematic investigation, where computed XA spectra are compared with the experiment, indicates elongation of the C-H bond pointing toward the surface to 1.18+/-0.05 A. The bond elongation arises due to mixing between bonding and antibonding C-H orbitals. Computed charge density difference plots show that no covalent chemical bond is formed between the adsorbate and substrate upon adsorption. The changes in electronic structure arise in order to minimize the Pauli repulsion by polarizing charge away from the surface toward the carbon atom of the methane molecule.
利用角分辨X射线吸收光谱（XAS）并结合密度泛函理论光谱计算，对吸附在Pt(977)上的甲烷的电子结构进行了研究。XAS能特异性地探测未占据态，结果表明由于s-p重新杂化，出现了对称性禁阻的气相最低未占据分子轨道。此外，新的吸附诱导态出现在费米能级之上。通过将计算得到的XA光谱与实验进行比较的系统研究表明，指向表面的C-H键伸长至1.18±0.05 Å。键的伸长是由于成键和反键C-H轨道之间的混合所致。计算得到的电荷密度差图表明，吸附时吸附质与基底之间未形成共价化学键。电子结构的变化是为了通过将电荷从表面向甲烷分子的碳原子极化来最小化泡利排斥。
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