Quiller R G, Baker T A, Deng X, Colling M E, Min B K, Friend C M
School of Engineering and Applied Sciences, Harvard University, 29 Oxford St., Cambridge, Massachusetts 02138, USA.
J Chem Phys. 2008 Aug 14;129(6):064702. doi: 10.1063/1.2965821.
We present evidence for the formation of transient hydroxyls from the reaction of water with atomic oxygen on Au(111) and investigate the effect of adsorbed oxygen on the hydrogen bonding of water. Water is evolved in peaks at 175 and 195 K in temperature programed reaction experiments following adsorption of water on oxygen-covered Au(111). The peak at 175 K is ascribed to sublimation of multilayers of water, whereas the peak at 195 K is associated with oxygen-stabilized water or a water-hydroxyl surface complex. Infrared reflection absorption spectra are consistent with the presence of molecular water over the entire range of coverages studied, indicating that isolated stable hydroxyls are not formed. Isotopic exchange of adsorbed (16)O with H(2)(18)O following adsorption and subsequent temperature programed reaction, however, indicates that transient OH species are formed. The extent of oxygen exchange was considerable--up to 70%. The degree of oxygen exchange depends on the initial coverage of oxygen, the surface temperature when preparing oxygen adatoms, and the H(2)(18)O coverage. The hydroxyls are short-lived, forming and disproportionating multiple times before water desorption during temperature programed reaction. It was also found that chemisorbed oxygen is critical in the formation of hydroxyls and stabilizing water, whereas gold oxide does not contribute to these effects. These results identify transient hydroxyls as species that could play a critical role in oxidative chemical reactions on gold, especially in ambient water vapor. The crystallinity of adsorbed water also depended on the degree of surface ordering and chemical modification based on scanning tunneling microscopy and infrared spectra. These results demonstrate that oxidation of interfaces has a major impact on their interaction with water.
我们展示了水与Au(111)表面的原子氧反应形成瞬态羟基的证据，并研究了吸附氧对水氢键的影响。在温度程序反应实验中，水吸附在氧覆盖的Au(111)上后，在175 K和195 K出现水脱附峰。175 K处的峰归因于多层水的升华，而195 K处的峰与氧稳定的水或水 - 羟基表面络合物有关。红外反射吸收光谱与在所研究的整个覆盖范围内存在分子水一致，表明没有形成孤立的稳定羟基。然而，吸附的(16)O与H(2)(18)O在吸附及随后的温度程序反应后的同位素交换表明形成了瞬态OH物种。氧交换程度相当可观——高达70%。氧交换程度取决于氧的初始覆盖度、制备氧原子时的表面温度以及H(2)(18)O的覆盖度。在温度程序反应过程中，羟基寿命短暂，在水脱附之前会多次形成和歧化。还发现化学吸附的氧对于羟基的形成和水的稳定至关重要，而氧化金对此没有贡献。这些结果表明瞬态羟基可能在金表面的氧化化学反应中起关键作用，特别是在环境水蒸气存在的情况下。基于扫描隧道显微镜和红外光谱，吸附水的结晶度还取决于表面有序度和化学修饰程度。这些结果表明界面氧化对其与水的相互作用有重大影响。
