Temperature Dependence of the Near-Edge Spectrum of Water

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• 作者：Tuomas Pylkk盲nen ; Arto Sakko ; Mikko Hakala ; Keijo H盲m盲l盲inen ; Giulio Monaco ; Simo Huotari
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：December 15, 2011
• 年：2011
• 卷：115
• 期：49
• 页码：14544-14550
• 全文大小：879K
• 年卷期：v.115,no.49(December 15, 2011)
• ISSN：1520-5207

文摘

The interpretation of the oxygen near-edge spectrum of water has been debated intensively. We present new measurements of the temperature dependence of the spectrum and perform a van鈥檛 Hoff analysis for the pre-edge intensity. Many microscopical and thermodynamic properties of liquid water have been described in the literature in terms of mixture models, which presume the existence of two distinct species with different local structures. Assuming such a two-component model here leads to a van鈥檛 Hoff enthalpy change 螖H = 0.9 卤 0.2 kcal/mol for the conversion between the two presumed components contributing to the pre-edge intensity. The small value of 螖H compared to the average bond energy implies that the components are nearly equally bonded, suggesting that the pre-edge is sensitive to structural changes that leave hydrogen bonds intact. We further show that the pre-edge intensity in the vapor, liquid, and ice Ih spectra can be correlated with enthalpy changes. While the pre-edge intensity in water has often been interpreted to imply a large fraction of broken hydrogen bonds in the liquid, we propose that the current results indicate that those bonds would not be considered broken by energetical criteria.