Abstract
本論文主要是利用表面紅外光譜與循環伏特安培法來研究一氧化碳以及一 氧化氮在過渡金屬單晶電極上之吸附和氧化還原反應。一氧化碳在 Ir(111)和Ir(110)單晶上僅存在單一吸附位，其紅外光譜之振動頻率、吸 收峰強度以及波寬會隨著表面覆蓋度而改變，此種在電化學環境下之紅外 光譜行為被用來與真空環境下所得者做一比較，藉以了解溶劑和表面電位 所帶來的影響。兩個環境下振動頻率的不同可以由校正電化學和真空環境 下之電位差異來消除，而吸收強度與波寬之差別主要係來自於溶劑(水)的 影響。利用表面紅外光譜，一氧化氮吸附於Pt、Rh及Ir單晶電極，在電化 學以及真空環境下之振動光譜行為同時亦是研究之主題。除了研究一氧化 碳與一氧化氮個別的吸附之外，本論文並探討了此兩種氣體在單晶電極表 面之共吸附。在所研究的六個單晶表面，與飽和之吸附層相比，共吸附之 一氧化碳和一氧化氮，其振動頻率皆降低；而一氧化氮在共吸附時更是大 幅下降。這種振動頻率皆降低與吸收強度改變之現象，即是吸附物均勻混 合之證明。在Pt和Rh表面，一氧化氮會促使一氧化碳的吸附位改變，傾向 於吸附於原子頂端(atop)，這可能是由於一氧化氮具有較強之back p bonding，在多原子吸附位較強之原因。所研究之單晶電極，一氧化碳和 一氧化氮之共吸附，基本上皆是呈均勻混合而非聚集分離；本研究並進行 偶極耦合模型之理論計算，以輔助證明實驗結果之推論。 Cyclic voltammetry and in-situ infrared reflection-absorption spectroscopy(IRAS)have been employed to characterize the adsorbed and catalytic behavior of CO andNO on various platinum- group single-crystal surfaces. Infrared spectra measuredfor he C-O stretch of CO on Ir(111) and Ir(110) in acid solution as a function of the dosed coverage are compared with corresponding extant IRAS data in ultrahigh vacuum (UHV), in order to elucidate the physical influences exerted by theelectrochemical double-layer environment on chemisorbate vibrational properties.The nature of the vibrational interaction is accessed in part by comparing thecoverage-dependent spectral parameters with predictions from a numerical dipole-dipole calculation. Comparisons are also made with the NO spectra on severalPt-group surfaces in electrochemical and vacuum environments. In addition toexamining CO and NO adsorption separately, the microscopic nature of mixed NO/COadlayers on low-index Pt-group metals was also explored. Progressive displacementof NO by exposing NO-saturated electrodes to dilute CO solutions yielded chieflymolecularly intermixed CO/NO adlayers for all the pt- group electrodes examined.On Rh(100), Rh(111), Pt(111) and Pt(100), NO coadsorption induces CO "bridging" to "atop" site switching. This is largely consistent with the formation of molecular intermixed CO/NO adlayers where the strong preference of NO formultifold site shifts CO molecules into neighbouring atop-like configurations.On Pt(111) and Rh(111), however, the CO spectral fingerprints for the CO/NO adadlayers suggest the additional presence of segregated compressed "CO-rich"domains.