Observation of the Chemical Structure of Water up to the Critical Point by Raman Spectroscopic Analysis of Fluid Inclusions
Observation of the Chemical Structure of Water up to the Critical Point by Raman Spectroscopic Analysis of Fluid Inclusions
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通过流体包裹体的拉曼光谱分析观察水的化学结构直至临界点
DOI：
10.1021/acs.jpcb.9b02129
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发表时间：
2019
影响因子：
3.3
通讯作者：
Charles Le Losq
中科院分区：
文献类型：
--
作者：
lizhou;Terrence Patrick Mernagh;Charles Le Losq
从石英中合成包裹体中的临界密度(322 kg·m-3)下捕获的纯水的液、汽相同时获得了拉曼光谱。当这些包裹体被加热到临界温度(373.946℃)时，液相密度降低，而拉曼OH伸展带的最大值随波数增加而增大。相反，随着气相密度的增加，拉曼OH-伸缩带的最大值随波数减小而减小。在水的临界点，液体和汽相的拉曼光谱汇聚成一个单一的谱带，在那里流体以单一的相存在。水的气相和液态的带心比较表明，随着密度的增加和减少，这些相中的氢键量分别增加和减少。通过用五个高斯分量对拉曼OH-拉曼伸缩峰进行峰拟合，进一步量化了这些影响。除双施主-单受主(H2O)4团簇外，其余各组分的拉曼光谱均随温度的升高而减小，但在300℃以上时，双施主-单受主(H2O)4团簇的拉曼光谱最强。在300℃以下，气相的拉曼光谱主要由游离的OH组分主导，但在此温度以上，双施主-单受主(H2O)4团簇仍是最强的谱带。结果表明，在高温下，液态水和蒸汽水中都存在大量的水团簇，超临界水可认为是由双施主-单受主(H2O)4团簇组成的小水团簇[(H2O)n，n=1-4]的混合物。
Raman spectra were obtained simultaneously from the liquid and vapor phases of pure water trapped at the critical density (322 kg·m–3) within synthetic inclusions in quartz. As these inclusions are heated up to the critical temperature (373.946 °C), the liquid phase decreases in density and the maximum of the Raman OH-stretching band increases in wavenumber. Conversely, as the vapor phase increases in density, the maximum of the Raman OH-stretching band decreases in wavenumber. The Raman bands of the liquid and vapor phases converge to a single band at the critical point of water, where the fluid exists as a single phase. A comparison of the band centroids for the vapor and liquid phases of water indicates respective increases and decreases in the amount of hydrogen bonding in these phases as a function of increasing and decreasing density. These effects were further quantified by peak-fitting the Raman OH-stretching peak with five Gaussian components. All the Gaussian components of the liquid phase decrease in amplitude with increasing temperature with the exception of the double donor–single acceptor (H2O)4cluster, which increases in amplitude and becomes the most intense component at temperatures above 300 °C. The Raman spectra of the vapor phase are dominated by the free OH component at temperatures below 300 °C, but, above this temperature, the double donor–single acceptor (H2O)4cluster is again the most intense band. The results indicate that a significant quantity of water clusters is present in both liquid and vapor water at high temperatures and that supercritical water can be considered as a mixture of small water clusters [(H2O)n,n= 1–4] dominated by the double donor–single acceptor (H2O)4cluster.