Chaudhuri A, Odelius M, Jones R G, Lee T-L, Detlefs B, Woodruff D P
Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom.
J Chem Phys. 2009 Mar 28;130(12):124708. doi: 10.1063/1.3102095.
The local structure of the Au(111)(square root(3) x square root(3))R30 degrees-methylthiolate surface phase has been investigated by S K-edge near-edge s-ray absorption fine structure (NEXAFS) both experimentally and theoretically and by experimental normal-incidence x-ray standing waves (NIXSW) at both the C and S atomic sites. NEXAFS shows not only excitation into the intramolecular sigma() S-C resonance but also into a sigma() S-Au orbital perpendicular to the surface, clearly identifying the local S headgroup site as atop a Au atom. Simulations show that it is not possible, however, to distinguish between the two possible adatom reconstruction models; a single thiolate species atop a hollow-site Au adatom or a dithiolate moiety comprising two thiolate species bonded to a bridge-bonded Au adatom. Within this dithiolate moiety a second sigma() S-Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the sigma() S-C resonance. The new NIXSW data show the S-C bond to be tilted by 61 degrees relative to the surface normal, with a preferred azimuthal orientation in <211>, corresponding to the intermolecular nearest-neighbor directions. This azimuthal orientation is consistent with the thiolate being atop a hollow-site Au adatom, but not consistent with the originally proposed Au-adatom-dithiolate moiety. However, internal conformational changes within this species could, perhaps, render this model also consistent with the experimental data.
通过硫 K 边近边 X 射线吸收精细结构（NEXAFS），从实验和理论两方面对 Au(111)(√3×√3)R30°-甲硫醇盐表面相的局部结构进行了研究，并通过在 C 和 S 原子位点的实验性正入射 X 射线驻波（NIXSW）进行了研究。NEXAFS 不仅显示出激发到分子内σ* S-C 共振，还显示出激发到垂直于表面的σ* S-Au 轨道，清楚地确定了局部 S 头基位点位于 Au 原子之上。然而，模拟表明，无法区分两种可能的吸附原子重构模型：一种是位于空心位点 Au 吸附原子上的单个硫醇盐物种，另一种是由两个硫醇盐物种键合到桥连 Au 吸附原子上的二硫醇盐部分。在这个二硫醇盐部分内，一个几乎平行于表面的第二个σ* S-Au 轨道具有与σ* S-C 共振重叠的较高能量。新的 NIXSW 数据表明，S-C 键相对于表面法线倾斜 61°，在<211>方向上具有优先方位取向，对应于分子间最近邻方向。这种方位取向与硫醇盐位于空心位点 Au 吸附原子上一致，但与最初提出的 Au-吸附原子-二硫醇盐部分不一致。然而，该物种内部的构象变化可能使该模型也与实验数据一致。
