中文摘要

本篇論文是以程序控溫反應/脫附(TPR/D)和反射式吸收紅外光譜(RAIRS)來研究在超高真空系統中β-halohydrins (XCH2CH2OH, X=F,Cl,Br,I)在Cu(100)表面上的吸附與反應。擁有一個OH基的乙醇在Cu(100)上進行可逆吸附而無法分解；在鹵化乙烷方面，經由碳鹵鍵的斷裂，在表面上形成鹵素和乙基，乙基在表面上進行β-hydride elimination形成乙烯；至於氯化烷類則要等到7個碳的長度才能使C-Cl鍵在銅表面上斷裂。在此我們要研究同時擁有鹵素及OH基的β-halohydrins的熱化學反應。在TPR/D的實驗中2-碘乙醇會分解產生水、乙烯、乙醇、乙醛、丁烷及1,4-dioxane，但是在未滿單層分子吸附量之下，並無發現分子性脫附；在2-溴乙醇的例子中，最主要脫附的產物為水、乙烯、乙醛、1,4-dioxane及溴乙烷，而且我們也未發現單層分子性脫附；在2-氯乙醇的例子裡，其生成的產物不同於2-碘乙醇和2-溴乙醇，在TPR/D中顯示乙烯、氯乙烯、少許水及單層分子性脫附等熱化學產物；在2-氟乙醇的例子中，其水、乙烯及1,4-dioxane等產物相對量較其他的低。在RAIRS的實驗中，發現2-碘乙醇在低溫時會反應形成hydroxyethyl的物種，到200K時便形成(–OCH2CH2–)的中間体；在2-溴乙醇的例子中，我們並未發現hydroxyethyl的中間体，但在200K時也觀察到(–OCH2CH2–)中間体的形成；在2-氯乙醇與2-氟乙醇中，我們並未發現任何穩定的中間体，在低覆蓋量中，它們是以gauche form吸附在表面上。

Abstract

Temperature-programmed reaction/desorption (TPR/D) and reflection-absorption infrared spectroscopy have been employed to investigate the adsorption and reactions of β-halohydrins (XCH2CH2OH, X=F,Cl,Br,I) on a Cu(100) surface under ultrahigh vacuum condition. With a OH group, ethanol adsorbs reversibly on Cu(100). In the case of halogenated ethane, ethyl iodide and ethyl bromide decompose via carbon-halogen bond scission to generate halogen atoms and ethyl groups on the surface. Ethyl groups undergo β-hydride elimination to form ethylene. Unlike alkyl iodide and bromide, C-Cl bond dissociation of alkyl chloride dose not occur until the chain length reaches seven carbons. Here we study the thermal chemistry of β-halohydrins with the two functional groups of OH and X. In TPR/D experiments 2-iodoethanol decomposes to produce water, ethylene, ethanol, acetaldehyde, butane, and 1,4-dioxane. But we can not find molecular desorption at submonolayer coverage. For the 2-bromoethanol, the main desorbing products are water, ethylene, acetaldehyde, 1,4-dioxane, and bromoethane. We can not find the monolayer molecular desorption either. In the 2-chloroethanol case, the product distribution is different from those of 2-iodoethanol and 2-bromoethanol. TPR/D shows the thermal products of ethylene, chloroethene, some water, and monolayer molecular desorption. For the 2-fluoroethanol, the products of water, ethylene and 1,4-dioxane is relatively low. In RAIRS experiments, it is found that 2-iodoethanol reacts at relatively low temperature to form hydroxyethyl specie. At 200K, it forms the surface oxametallacycle (–OCH2CH2–) intermediate. In 2-bromoethanol case, we can not find hydroxyethyl intermediate on the surface, but obverse the oxametallacycle intermediate at 200K. In 2-chloroethanol and 2-fluoroethanol case, we do not find any stable intermediate. At low coverages, they adsorbs on the surface in gauche form.

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