Zhou X J, Li Q, Leung K T
Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
J Phys Chem B. 2006 Mar 23;110(11):5602-10. doi: 10.1021/jp056103r.
The room-temperature adsorption and thermal evolution of cis-dichloroethylene (DCE) and perchloroethylene (PCE) on Si(100)2 x 1 have been studied by X-ray photoelectron spectroscopy and temperature programmed desorption (TPD) mass spectrometry. Unlike ethylene that is found to adsorb on Si(100)2 x 1 through a [2+2] cycloaddition reaction, cis-DCE and PCE appear to dechlorinate upon adsorption on the 2 x 1 surface through an insertion reaction preserving the C=C bond. Our C 1s XPS spectra are consistent with the existence of mono-sigma-bonded and di-sigma bonded dechlorinated adstructures for both cis-DCE and PCE. The presence of the XPS C 1s feature at 283.9 eV, characteristic of the (=C<(Si)(Si)) component, supports the formation of a unique tetra-sigma-bonded C(2) dimer (i.e., by full dechlorination) for PCE, which is found to be stable to 800 K. In marked contrast to PCE for which no organic desorption fragments are observed, m/z 26 TPD features at 590 and 750 K have been observed for cis-DCE. These features could be attributed to the formation of acetylene resulting from Cl beta-elimination of 2-chlorovinyl adspecies and to direct desorption of vinylene, respectively. Further annealing the cis-DCE and PCE samples to above 800 K produces SiC and/or carbon clusters. The TPD data also show HCl evolution over 810-850 K for both cis-DCE and PCE, the latter of which also exhibits an additional SiCl(2) evolution above 850 K. The present work illustrates that the insertion mechanism could be quite common in the surface chemistry of chlorinated ethylenes on the 2 x 1 surface.
通过X射线光电子能谱和程序升温脱附（TPD）质谱研究了顺式二氯乙烯（DCE）和全氯乙烯（PCE）在Si(100)2×1表面上的室温吸附和热演化。与通过[2+2]环加成反应吸附在Si(100)2×1上的乙烯不同，顺式DCE和PCE在吸附到2×1表面时似乎通过保留C=C键的插入反应进行脱氯。我们的C 1s XPS光谱与顺式DCE和PCE的单σ键和双σ键脱氯吸附结构的存在一致。在283.9 eV处出现的XPS C 1s特征，即(=C<(Si)(Si))组分的特征，支持了PCE形成独特的四σ键C(2)二聚体（即通过完全脱氯），该二聚体在800 K时是稳定的。与未观察到有机脱附碎片的PCE形成显著对比的是，在590和750 K处观察到顺式DCE的m/z 26 TPD特征。这些特征可能分别归因于2-氯乙烯基吸附物种的Clβ消除产生乙炔以及亚乙烯基的直接脱附。将顺式DCE和PCE样品进一步退火至800 K以上会产生SiC和/或碳簇。TPD数据还显示，顺式DCE和PCE在810-850 K范围内都有HCl析出，后者在850 K以上还表现出额外的SiCl(2)析出。目前的工作表明，插入机制在2×1表面氯化乙烯的表面化学中可能相当普遍。
