Infrared electroabsorbtion spectroscopic study of water in 1,4-dioxane

• Main Authors: Shih, Hsi-Kang, 史習岡
• Other Authors: Shinsuke Shigeto
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/65643285291114024180

碩士 === 國立交通大學 === 應用化學系分子科學碩博士班 === 100 === Water is an exceedingly complicated liquid in both static and dynamic aspects. In the present study, we aimed to shed new light on the static molecular properties of water through investigating its response to an external electric field modulation. We studied the O–H stretch region of water dissolved in 1,4-dioxane using infrared (IR) electroabsorption spectroscopy. This technique is capable of detecting with high sensitivity the changes in IR absorption spectrum induced by an externally applied electric field. It provides quantitative information on molecular properties such as the permanent dipole moment and the polarizability, which sharply reflect the structure and local environments of the molecule. First, using a multivariate curve resolution approach, we analyzed a series of FT-IR spectra of water dissolved in 1,4-dioxane at different concentrations of water ranging from 0 to 2 M. The results show that the observed concentration-dependent spectra can be reproduced well by assuming two independent components. We assigned these components as isolated water species surrounded by 1,4-dioxane and those in small water ensemble (cluster). Next, we measured IR electroabsorption (?媚) spectra of the O–H stretch band of water dissolved in 1,4-dioxane. ?媚 signal of the order of 10−6 was successfully detected. We recorded the ?媚 spectrum by changing the angle, ??z between the direction of the applied field and the polarization vector of the IR light. The ??dependence of the ?媚 spectra was analyzed with a singular value decomposition approach, yielding the ??dependent and ??independent component spectra. Fitting analysis of both spectra suggests that, in contrast to other molecular liquids studied so far, water dissolved in 1,4-dioxane seems to respond to the electric field via the electronic polarization (i.e., changes in dipole moment and/or polarizability upon vibrational excitation) rather than orientational anisotropy.