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研究生： 郭冠宏
Kuo, Kuan-Hung
論文名稱： 1,2-二溴乙烷在Cu(100)表面上的熱反應與吸附位向的研究
Thermal Chemistry and Adsorption Orientation of 1,2-dibromoethane on Cu(100) Surface
指導教授： 林榮良
Lin, Jong-Liang
學位類別： 碩士
Master
系所名稱： 理學院 - 化學系
Department of Chemistry
論文出版年： 2004
畢業學年度： 92
語文別： 中文
論文頁數： 65
中文關鍵詞： 2-二溴乙烷 、程序控溫反應/脫附，反射式吸收紅外光譜，1
外文關鍵詞： TPR/D，RAIRS，BrCH2CH2Br
相關次數： 點閱：111  下載：11 
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    • 　　本篇論文是以程序控溫反應/脫附(Temperature-programmed reaction/desorption，TPR/D)和反射式吸收紅外光譜(reflection absorption infrared spectroscopy，RAIRS)技術，於超高真空系統中，研究BrCH2CH2Br分子在乾淨以及O原子覆蓋的Cu(100)表面上的熱反應與吸附位向。由TPR/D的結果顯示曝露量到了10L時，開始有來自第二層吸附的BrCH2CH2Br分子性的脫附出現在209K，曝露量增加到20L，在163K出現第三層BrCH2CH2Br分子的脫附。單分子層以下的BrCH2CH2Br曝露量，BrCH2CH2Br會在表面上分解形成C2H4脫附，曝露量0.5-6L時，C2H4有~210K的脫附峰，曝露量在2L以上時，C2H4有130K的脫附峰。曝露量在4-9L之間，C2H4在155至180K的範圍內也有脫附的管道。130K的C2H4脫附可能是因為BrCH2CH2Br分子以Br原子朝向表面的方式吸附，在斷了C-Br鍵後，C2H4分子沒有機會接觸到表面在低溫就脫附了。210K的C2H4可能是脫附所決定的 (desorption limited)，亦即BrCH2CH2Br分解後在表面形成C2H4，隨後溫度升高至較高溫才從表面脫附，此C2H4管道也許是來自缺陷位置上的脫附。在155-180K間脫附的C2H4是出現在≧4L的較高覆蓋率之下，因為從RAIRS得知140K時表面並沒有BrCH2CH2Br或-CH2CH2Br存在也就是說BrCH2CH2Br已分解在表面上產生C2H4，而其脫附受到表面Br原子的影響，而在155-180K間出現。在O原子覆蓋的Cu(100)表面上，曝露量在0.1L以上時，C2H4在140K和168K脫附。我們認為其和在乾淨的Cu(100)表面上，C2H4在130K和155-180K間的反應機制是一樣的。但是在O原子覆蓋的Cu(100)表面並沒有看到有高溫210K脫附的C2H4，推測可能是表面上的O 原子佔據了缺陷位置。曝露量到了3L時，開始有來自第二層吸附的BrCH2CH2Br分子性的脫附出現在230K，曝露量增加到15L，在185K出現第三層BrCH2CH2Br分子的脫附。 由RAIRS的結果我們推測在乾淨的Cu(100)表面上，BrCH2CH2Br的多層分子主要是以trans form吸附，單分子層以下的BrCH2CH2Br則是分解性的吸附在表面上，以-C-C-Br骨架躺下的位向吸附。在O原子覆蓋的Cu(100)表面上，BrCH2CH2Br的多層分子主要也是以trans form吸附，但曝露量在3L以下可能由於IR吸收訊號過小或是BrCH2CH2Br分子分解，我們看不到任何吸收。

    　　Temperature-programmed reaction/desorption (TPR/D) and reflection absorption infrared spectroscopy (RAIRS) have been employed to investigate the thermal reactions and adsorption geometry of BrCH2CH2Br molecules on clean and oxygen-precovered Cu(100) surfaces in ultra-high vacuum system. TPR/D results show that when exposure is increased to 10L, second layer BrCH2CH2Br molecular desorption appears at 209K and when exposure is increased to 20L, third layer BrCH2CH2Br molecular desorption appears at 163K. Below monolayer exposure, BrCH2CH2Br will decompose to gaseous C2H4 . Between 0.5-6L exposures, C2H4 desorbs at ~210K and among 2L exposure, C2H4 desorbs at 130K. Between 4-9L exposures, C2H4 has a desorption channel at 155-180K. C2H4 desorption at 130K maybe results from BrCH2CH2Br absorbs in Br atom toward surfaces, after C-Br bond scission, because C2H4 has no opportunity to touch surfaces so it desorbs at low temperature. C2H4 desorption at 210K is likely to be desorption limited that, BrCH2CH2Br docomposes to C2H4 (a), only to desorb at higher　temperature. This C2H4 desorption channel maybe comes from defect site desorption. C2H4 desorption at 155-180K appears at coverage ≧4L, because RAIRS results show that no BrCH2CH2Br or -CH2CH2Br exist on the surfaces at 140K, so BrCH2CH2Br already decomposes to C2H4 (a), and C2H4 desorption is stabilized by Br on the surfaces to desorb at 155-180K. On oxygen-precovered surfaces and among 0.1L exposure, C2H4 desorbs at 140K and 168K. We suggest the mechanism is the same as C2H4 desorption at 130K and 155-180K on clean Cu(100) surfaces. But on oxygen-precovered surface we don’t see C2H4 desorbs at 210K, we speculate that oxygen maybe occupies defect site. When exposure is increased to 3L, second layer BrCH2CH2Br molecular desorption appears at 230K and when exposure is increased to 15L, third layer BrCH2CH2Br molecular desorption appears at 185K. By RAIRS results we speculate that multilayer BrCH2CH2Br absorb in trans form mainly and below monolayer BrCH2CH2Br dissociatively absorb on the surfaces in -C-C-Br skeleton lay down on surfaces. On oxygen-precovered Cu(100), multilayer BrCH2CH2Br also absorb in trans form mainly, but below 3L exposure, we can’t observe any absorption peak which maybe due to IR absorption intensity too weak or decomposition of BrCH2CH2Br.

    第一章、緒論.............................................................................................................1 1.1 表面的定義......................................................................................................1 1.2 表面吸附..........................................................................................................1 1.3 真空的定義及應用..........................................................................................2 1.4 研究BrCH2CH2Br的動機.............................................................................3 第二章、表面研究之分析技術 2.1 歐傑電子能譜......................................................................................................6 2.2 低能量電子繞射.................................................................................................11 2.3 程式控溫反應/脫附............................................................................................13 2.4 反射式紅外光譜儀.............................................................................................15 第三章、實驗系統與方法 3.1 超高真空系統.....................................................................................................18 3.2 Cu(100)單晶表面的清潔及氧化表面的製備.....................................................20 3.3 藥品及其前處理.................................................................................................22 第四章、結果與討論 4.1 BrCH2CH2Br在Cu(100)表面上的吸附及反應................................................23 4.1.1 程序控溫反應/脫附實驗.................................................................................23 4.1.2 反射式吸收紅外光光譜實驗..........................................................................43 第五章、結論............................................................................................................61 參考文獻....................................................................................................................63

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