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Journal ArticleDOI

An optical cell for Raman spectroscopic studies of supercritical fluids and its application to the study of water to 500°C and 2000 bar

TL;DR: In this article, a high-temperature, high-pressure optical cell has been developed for the study of aqueous solutions by Raman spectroscopy, which has a sample volume of < 1 ml and utilizes diamond or sapphire windows set at 90° to one-another.
About: This article is published in Chemical Geology.The article was published on 1993-05-05. It has received 121 citations till now. The article focuses on the topics: Bar (unit) & Raman spectroscopy.
Citations
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Journal ArticleDOI
TL;DR: A detailed review of the major methods for determining fractionation factors can be found in this article, along with a discussion of the advantages and disadvantages of each of these methods in the context of stable isotope geochemistry.
Abstract: As demonstrated by the chapters in this short course, stable isotope techniques are an important tool in almost every branch of the earth sciences. Central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances. Indeed, it was Harold Urey’s (1947) thermodynamically based estimate of the temperature-dependence of 18O/16O fractionation between calcium carbonate and water, and a recognition of how this information might be used to determine the temperatures of ancient oceans, that launched the science of stable isotope geochemistry. The approach pioneered by Urey has since been used to estimate temperatures for a wide range of geological processes (e.g. Emiliani 1955; Anderson et al. 1971; Clayton 1986; Valley, this volume). In addition to their geothermometric applications, equilibrium fractionation data are also important in the study of fluid-rock interactions, including those associated with diagenetic, hydrothermal, and metamorphic processes (Baumgartner and Valley, this volume; Shanks, this volume). Finally, a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium, a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems (Cole and Chakraborty, this volume). In the fifty-four years since the publication of Urey’s paper, equilibrium fractionation data have been reported for many minerals and fluids of geological interest. These data were derived from: (1) theoretical calculations following the methods developed by Urey (1947) and Bigeleisen and Mayer (1947); (2) direct laboratory experiments; (3) semi-empirical bond-strength models; and (4) measurement of fractionations in natural samples. Each of these methods has its advantages and disadvantages. However, the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations, not all of which are in agreement. In this chapter, we evaluate the major methods for determining fractionation factors. …

431 citations

Journal ArticleDOI
TL;DR: In this paper, a potential model that employs diffuse charges, in addition to the usual point charges, on the oxygen and hydrogen atoms, to account for charge penetration effects was developed.
Abstract: With the objective of improving the effective pair potentials for water, we develop a potential model that employs diffuse charges, in addition to the usual point charges, on the oxygen and hydrogen atoms, to account for charge penetration effects. The potential has better transferability from the liquid to gaseous phases since, unlike many existing models, it does not require an enhanced dipole moment. As a result it accurately reproduces the structural and thermodynamic properties of water over a wide range of conditions. Moreover, by allowing for electronic polarization when evaluating the total dipole moment of the simulated fluid, the model leads to the correct value of the dielectric constant for virtually any state point. At room temperature the calculation produces an average dipole moment of 3.09 D, in accord with recent theoretical and experimental evaluations. This supports the idea that induction effects in water are more important than previously expected.

140 citations

Journal ArticleDOI
TL;DR: The Raman spectra of water under high temperature and pressure conditions are reported and show a discontinuity in the pressure dependence of the OH stretching frequency, which suggests a possible structural change under these conditions.
Abstract: We report on the Raman spectra of water under high temperature and pressure conditions and show a discontinuity in the pressure dependence of the OH stretching frequency. As pressure increases, the strength of hydrogen bonding increases rapidly in the pressure ranges up to 0.4±0.1 GPa at 25 °C, 1.0±0.1 GPa at 100 °C, and 1.3±0.1 GPa at 300 °C and slowly above these pressures. This finding clearly demonstrates the existence of discontinuities in the pressure response of the hydrogen bonds of water, which suggests a possible structural change under these conditions.

128 citations

Journal ArticleDOI
TL;DR: According to the simulations, distortions of the hydrogen-bond network increase dramatically when temperature and pressure increase to the supercritical regime and the average number of hydrogen bonds per molecule decreases.
Abstract: We report on the microscopic structure of water at sub- and supercritical conditions studied using X-ray Raman spectroscopy, ab initio molecular dynamics simulations, and density functional theory. Systematic changes in the X-ray Raman spectra with increasing pressure and temperature are observed. Throughout the studied thermodynamic range, the experimental spectra can be interpreted with a structural model obtained from the molecular dynamics simulations. A spatial statistical analysis using Ripley’s K-function shows that this model is homogeneous on the nanometer length scale. According to the simulations, distortions of the hydrogen-bond network increase dramatically when temperature and pressure increase to the supercritical regime. In particular, the average number of hydrogen bonds per molecule decreases to ≈0.6 at 600 °C and p = 134 MPa.

127 citations

Journal ArticleDOI
TL;DR: In this article, Duan et al. used Raman spectroscopy to calculate the composition of the aqueous liquid phase coexisting with the vapour phase in the synthetic fluid inclusions.

110 citations

References
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Book
01 Jan 1969
TL;DR: The Water Molecule 2 The Real Vapour 3. Ice 4. Properties of Liquid Water 5. Models for Liquid Water Addendum as mentioned in this paper, which is an extension of the model presented in this paper.
Abstract: 1. The Water Molecule 2. The Real Vapour 3. Ice 4. Properties of Liquid Water 5. Models for Liquid Water Addendum

2,886 citations

Journal ArticleDOI
TL;DR: In this paper, a new picture of water as consisting of flickering clusters of hydrogen-bonded molecules is presented, in which the cooperative nature of cluster formation and relaxation is related to the partially covalent character which is postulated for the hydrogen bond.
Abstract: : In addition to the direct action of the ionic charge on water as a dielectric medium, ions may exert an influence on the equilibrium between the ice-like and non-ice-like forms which are present in room-temperature water. This provides a way of accounting for experimental results in a variety of areas, including entropy, heat capacity, temperature of maximum density, tracer selfdiffusion, thermal conductivity, and dielectric relaxation, as well as viscosity and ionic mobility and their temperature coefficients. The tetrabutyl ammonium cation acts as a structure-promoter in the same way as do non-polar solutes, amino acids and fatty acid anions. These various effects seem explicable in a straightforward manner in terms of a new picture of water as consisting of flickering clusters of hydrogen-bonded molecules, in which the cooperative nature of cluster formation and relaxation is related to the partially covalent character which is postulated for the hydrogen bond. (Author)

1,577 citations

Journal ArticleDOI
TL;DR: In this paper, spectra of heavy water have been obtained under high resolution between 1.25-4.1μ (2400-8000 cm-1) and approximately 4500 lines have been measured, and the majority of them analyzed into ten bands of D2O and nine bands of HDO.
Abstract: Spectra of heavy water have been obtained under high resolution between 1.25—4.1μ (2400—8000 cm—1). Approximately 4500 lines have been measured, and the majority of them analyzed into ten bands of D2O and nine bands of HDO. The analysis is described in some detail, spectra of all bands are shown and a partial table of lines and a complete table of energy levels are presented. The vibration‐rotation constants are derived and compared with those of H2O.

1,234 citations

Journal ArticleDOI
TL;DR: In this paper, the authors derived the thermodynamic parameters of liquid water by means of a statistical thermodynamic treatment, based on the ''flickering cluster'' model proposed by Frank and Wen.
Abstract: The thermodynamic parameters of liquid water are derived by means of a statistical thermodynamic treatment, based on the ``flickering cluster'' model proposed by Frank and Wen. Various models proposed for the structure of liquid water are reviewed, and the advantages of the Frank—Wen model are pointed out. The hydrogen‐bonded ice‐like clusters of H2O molecules in equilibrium with non‐hydrogen‐bonded liquid are described quantitatively in terms of the molecular species participating in different numbers of hydrogen bonds in the clusters. Equations expressing the mole fractions of the various species in terms of the average cluster size are derived. The partition function derived for the description of liquid water is based on a distribution of the H2O molecules over five energy levels, corresponding to four, three, two, one, and no hydrogen bonds per molecule. The most probable values of the average cluster size, the mole fraction of non‐hydrogen‐bonded water, and the thermodynamic parameters are obtained ...

991 citations

Journal ArticleDOI
TL;DR: In this paper, a simple model based on connectivity concepts from correlated site percolation theory was proposed to examine the physical implications of the continuous hydrogen-bonded network formed by water molecules.
Abstract: The unusual low‐temperature behavior of liquid water is interpreted using a simple model based upon connectivity concepts from correlated‐site percolation theory. Emphasis is placed on examining the physical implications of the continuous hydrogen‐bonded network (or ’’gel’’) formed by water molecules. Each water molecule A is assigned to one of five species based on the number of ’’intact bonds’’ (the number of other molecules whose interaction energy with A is stronger than some cutoff VHB). It is demonstrated that in the present model the spatial positions of the various species are not randomly distributed but rather are correlated. In particular, it is seen that the infinite hydrogen‐bonded network contains tiny ’’patches’’ of four‐bonded molecules. Well‐defined predictions based upon the putative presence of these tiny patches are developed. In particular, we predict the detailed dependence upon (a) temperature, (b) dilution with the isotope D2O, (c) hydrostatic pressure greater than atmospheric, and...

721 citations