A RAIRS AND HREELS STUDY OF ACETONE ON PT(111)
A RAIRS AND HREELS STUDY OF ACETONE ON PT(111)
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DOI：
10.1016/0039-6028(91)90632-3
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发表时间：
1991-08-01
期刊：
影响因子：
1.9
通讯作者：
IBACH, H
中科院分区：
文献类型：
--
作者：
VANNICE, MA;ERLEY, W;IBACH, H
利用反射-吸收红外光谱法首次获得了丙酮吸附在无载体金属表面的红外光谱。这些结果得到了HREELS的补充。两组光谱给出的多层丙酮的峰位与液相丙酮的峰位非常相似，而eta-1（“末端”配位）单层状态的C = O伸缩频率红移至1638 cm-1，因此很容易识别。在这种基本上无缺陷的Pt（111）表面上，不容易获得eta-2物质的直接证据，因为没有先前报道的Pt（111）、Pd（111）和Ru（001）表面的高能结合态。然而，在1 K/s下，199 K下的第二个解吸峰可以从184 K下的较大的eta-1峰分辨出来。这些热脱附光谱还表明在脱附期间没有发生丙酮分解。这种更强结合的丙酮物质与eta-2物质相关联，但与其他物质相比，该表面上的小结合能差（1 kcal/mol）似乎较小，并且增加了分离该eta-2状态的难度。RAIRS和HREELS提供了除eta-1相以外的单层物质的其他证据。首先，最初形成的eta-1物质随着多层相的发展而逐渐消失。第二，在闪蒸到低于200 K的温度后，1638 cm-1的谱带被去除，但与甲基相关的1086、1360和1428 cm-1处的峰不仅被保留，而且强度增加，并且在1500和1610 cm-1之间出现新的谱带。最后，在异丙醇解离吸附得到吸附的氢和丙酮后，也形成这些后一个谱带。
The use of RAIRS (reflection-absorption infrared spectroscopy) has provided the first IR spectra of acetone adsorbed on an unsupported metal surface. These results were complemented by HREELS. Both sets of spectra gave peak positions for multilayer acetone that were very similar to those associated with liquid-phase acetone, whereas the eta-1 ("end-on" coordination) monolayer state had a C = O stretch frequency red-shifted to 1638 cm-1, thus making it easy to identify. Direct evidence for an eta-2 species, which has been proposed to exist in a "side-on" configuration with its C = O bond parallel to the surface, was not easy to obtain on this essentially defect-free Pt(111) surface because of the absence of higher-energy binding states that have been previously reported for Pt(111), Pd(111) and Ru(001) surfaces. However, at 1 K/s a second desorption peak at 199 K could be resolved from the larger eta-1 peak at 184 K. These thermal desorption spectra also indicated that no acetone decomposition occurred during desorption. This more strongly bound acetone species is associated with an eta-2 species, but the small binding energy difference (1 kcal/mol) appears to be less on this surface compared to the others and increases the difficulty of isolating this eta-2 state. Additional evidence for a monolayer species other than the eta-1 phase was provided by RAIRS and HREELS. First, the eta-1 species that initially forms gradually disappears as the multilayer phase develops. Second, after flashing to temperatures below 200 K the 1638 cm-1 band is removed, yet peaks at 1086, 1360, and 1428 cm-1, associated with the methyl groups, not only are retained but also grow in intensity, and new bands appear between 1500 and 1610 cm-1. Finally, these latter bands are also formed after the dissociative adsorption of isopropyl alcohol to give adsorbed hydrogen and acetone.