利用電場變調紅外線吸收光譜研究化學平衡：從簡單的液體系統到複雜的油包水乳液

Abstract

這篇論文主要是利用電場變調紅外線吸收光譜偵測兩種凝態系統的化學平衡，針對1,2-二溴乙烷以及反微胞系統中的水兩種系統分別進行研究。第一個主題是研究1,2-二溴乙烷間扭式/反式間異構化平衡的反應，藉由得到的熱力學參數，可求得室溫下的平衡常數 為0.33 (±0.04)，所以反應是趨向反式異構物；接著利用已知的熱焓差 ，可以得到兩種異構物間互相轉換的吉布斯自由能差 和熵差 ，分別是4.5 (±0.3) kJ mol−1 and −2.7 J K−1 mol−1。第二部分主題是研究以界面活性劑(磺化琥珀酸二辛酯鈉)與水所組成的反微胞系統，探討水分子中羥基伸縮模式的電場變調紅外線吸收光譜。從光譜的結果得知，加電場後吸收光譜的變化，呈現一正一負兩種不同性質的圖形。且羥基伸縮模式的吸收光譜可以利用三個不同的高斯分佈曲線加以擬合，這三種分佈曲線的特性代表水分子在反微胞中大致具有三種不同的氫鍵環境，所以經由電場變調紅外線吸收光譜可以偵測不同型態水分子在反微胞內的分佈情形。

Infrared (IR) electroabsorption spectroscopy is used to study chemical equilibria of the two condensed-phase systems: liquid 1,2-dibromoethane and water in reverse micelles. First, we report on experimental determination of thermodynamic parameters associated with the gauche/trans conformational equilibrium of liquid 1,2-dibromoethane. The equilibrium constant at room temperature was determined to be 0.33 (±0.04), which indicates that the trans conformer is energetically more favored than the gauche conformer. With the reported value of the enthalpy difference , we obtained the Gibbs free energy difference and the entropy difference between the two conformers as 4.5 (±0.3) kJ mol−1 and −2.7 J K−1 mol−1, respectively. In the second system, we measured IR electroabsorption spectra in the OH stretching region of water in aerosol OT reverse micelles. The observed IR electroabsorption spectrum shows a bipolar feature with intensity moving from the red to the blue. The OH stretching absorption band is deconvoluted to three Gaussian subbands, which correspond to distinct hydrogen-bonding environments. The IR electroabsorption spectrum may be interpreted in terms of a field-induced population change among those three kinds of water molecules, which are assumed to occur in equilibrium.