TY - JOUR
T1 - Observation of the Chemical Structure of Water up to the Critical Point by Raman Spectroscopic Analysis of Fluid Inclusions
AU - Zhou, Li
AU - Mernagh, Terrence Patrick
AU - Le Losq, Charles
N1 - Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/6/12
Y1 - 2019/6/12
N2 - 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)4 cluster, 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)4 cluster 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)4 cluster.
AB - 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)4 cluster, 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)4 cluster 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)4 cluster.
UR - http://www.scopus.com/inward/record.url?scp=85068441788&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcb.9b02129
DO - 10.1021/acs.jpcb.9b02129
M3 - Article
SN - 1520-6106
VL - 123
SP - 5841
EP - 5847
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 27
ER -