G. E. Walrafen

RAMAN SPECTRAL STUDIES OF WATER STRUCTURE

Raman frequencies and polarizations and infrared frequencies of water and heavy water have been obtained, and the intermolecular vibrations of water have been related to a five‐molecule hydrogen‐bonded C2v model consistent with x‐ray data. Observed variations of the integrated Raman intensity of the 175‐cm—1 hydrogen‐bond‐stretching vibration, with variations of temperature, have been interpreted in terms of the five‐molecule model. That interpretation leads to reasonable values for the enthalpy of hydrogen‐bond formation. Effects of electrolyte addition on the intensity of the 175‐cm—1 band are also described.

Raman Spectral Studies of the Effects of Temperature on Water Structure

Integrated Raman intensities of the spectral contour arising from the intermolecular librational motions of pure water have been obtained in the temperature range of ∼10°—95°C. In addition, integrated intensities of nearly symmetric librational components centered near ∼475 and ∼710 cm−1 were obtained from manual contour analysis according to two components. However, contour analysis was also accomplished by means of a special‐purpose analog computer, and three Gaussian librational components having average frequencies of 439, 538, and 717 cm−1 were thus revealed. The total contour intensity, the manually determined component intensities, and the Gaussian component intensities were found to have the same temperature dependence, and that dependence was found to be in excellent quantitative agreement with the previously reported temperature dependence of the hydrogen‐bond‐stretching intensity [J. Chem. Phys. 44, 1546 (1966)]. Integrated Raman intensities of pure water were also obtained in the temperature r...

Water and its relation to broken bond defects in fused silica

We have studied the effects of water and defects on the Raman spectrum of fused silica. Intensities of defect lines at 604 and 490 cm−1 were found to increase with fictive temperature and to decrease with increasing OH content. The results suggest that water in the melt is preferentially trapped at the defect sites. The increased sensitivity obtained by using an optical fiber as the sample enabled us to see for the first time the Si– (OH) stretching vibration at 970 cm−1. The Si–(OH) intensity agrees with that of the 1100 cm−1 dangling oxygen line in a silica fiber weakly doped with K2O. A comparison with other spectral features shows that the Raman cross section for the Si–O stretch is extremely weak. This weak cross section contributes to the weak Raman intensity of the 1100 cm−1 lines in both fused and crystalline SiO2 and also explains why the dangling oxygen stretching vibration is not observed by Raman scattering in neutron damaged silica. Measurements of the much stronger 3690 cm−1 OH stretching vi...

Raman Spectral Studies of the Effects of Electrolytes on Water

Photoelectric Raman spectra of water at temperatures from 2° to 94°C have been obtained for the spectral region of about 0–4000 cm—1. Comparisons of these spectra, with Raman spectra of bromide and chloride solutions, indicate that certain intensities, which are increased by lowering the temperature of water, are also increased by electrolyte addition. Such intensity increases of Raman bands of the bromide and chloride solutions appear to be related to the ordering of water and ions. Other Raman bands of water, for which intensity increases occur with lowering of temperature, decrease in intensity with electrolyte addition. Those effects apparently are related to O–H···O bonds.The intensities of various bands studied, e.g., the librational bands, were observed to increase linearly with electrolyte concentration. In addition, marked intensity increases with increasing anionic size, i.e., Br—>Cl—, were observed, but the effects of the cations, while similar with respect to increasing size, appear to be rela...

Raman Spectral Studies of the Effects of Temperature on Water and Electrolyte Solutions

All known intermolecular Raman bands of water, viz., the hydrogen‐bond bending and stretching bands, and the librational bands, decrease rapidly in intensity with temperature rise. In contrast, the librational intensities of water in electrolyte solutions exhibit very small variations with temperature. The intensity decreases observed for pure water indicate that hydrogen bonds are broken by increase of temperature, but the near constancy observed for solutions indicates that primary hydration is not greatly affected, even at temperatures near the normal boiling points of some of the solutions studied.Integrated Raman intensities of the hydrogen‐bond‐stretching vibrations of pure water at 152–175 cm−1 were redetermined in the temperature range of −6.0° to 94.7°C. The new intensity data, which are more accurate than the old [cf., J. Chem. Phys. 40, 3249 (1964)], yield the values ΔH°=5.6 kcal/mole and ΔS°≈19 cal/deg·mole for the process B→U, where B refers to water molecules which contribute intensity to th...

Raman Spectral Studies of the Effects of Perchlorate Ion on Water Structure

Raman contours corresponding to the OD and OH stretching vibrations from HDO, as well as from H2O and D2O, were obtained at 25°C from a series of ternary aqueous solutions containing HDO, ClO4− (Li+, Na+, K+), and H2O or D2O. The Raman spectra were obtained photoelectrically using 4880‐A argon‐ion‐laser excitation, as well as conventional 4358‐A mercury excitation. Quantitative Raman data were obtained from ternary solutions having NaClO4 concentrations from 1 to 4M, and stoichiometric concentrations of 5.51M D2O (H2O as solvent), or 5.53M H2O (D2O as solvent). Raman spectra were also obtained from solutions having lower (and higher) HDO or NaClO4 concentrations. In addition, binary solutions of NaClO4 and H2O or D2O were examined. Addition of ClO4− to solutions containing HDO, and H2O or D2O produces a pronounced splitting of the OD and OH stretching contours from HDO, as well as from D2O and H2O. The splittings are directly observable in the Raman spectra. Two principal peaks or components, having frequ...

Raman Spectral Studies of the Effects of Solutes and Pressure on Water Structure

Raman spectra excited by 4800‐A argon‐ion‐laser radiation and recorded photoelectrically have been obtained from a series of ternary aqueous solutions by back scattering and by 90° scattering using Cary and Jarrell–Ash double monochromators, respectively. The OD stretching region of HDO (and D2O), 2300–2800 cm−1, and the OH stretching region of H2O plus HDO, ∼ 2800–3800 cm−1, were examined for the following solutes: (1) NaPF6, (2) NaSbF6, (3) NaClO4, (4) NaBF4, (5) NaReO4, (6) NaMnO4 (infrared only), (7) NaIO4, (8) NaNO3, (9) NaClO3, (10) NaSCN, (11) KI, (12) CsF, (13) Na2SO4, (14) (C4H9)4NCl, and (15) Xe. (See Addendum for other solutes.) In addition, Raman spectra were obtained from HDO in H2O at pressures from 1 to 3790 bar at 25°C, and from a 5.0M solution of NaClO4 in HDO and H2O at pressures of 690 and 3450 bar at 25°C. Several pronounced intensity maxima were observed in the OD and OH stretching regions for salts of extremely strong acids, (1)–(4), and some qualitative correlations with the strengt...

Raman Spectral Studies of HTO in H2O

Argon‐ion laser Raman spectra have been recorded photoelectrically from a 10 volume % solution of T2O in H2O at temperatures from 26 to 94°C and from a 3.6M ternary solution of NaClO4 in 5 volume % T2O in H2O at 25°C. Laser‐Raman spectra were also obtained from a 10 volume % solution of H2O in D2O at temperatures from ·23 to 96°C. At 26°C, a Raman intensity maximum was observed in the OT stretching region from HTO near Δ ν=2130 ± 5 cm−1, and a shoulder was apparent near Δ ν=2225 − 2250 cm−1. An isosbestic frequency was also indicated for HTO near Δ ν=2164 ± 7 cm−1 from 26 to 70°C and for HDO near 3450 cm−1 from ·23 to 63°C. The shapes of the OT and OH stretching contours from HTO and HDO were approximated by two broad Gaussian components using an analog computer, and the resulting plots of log10 (INHB / IHB) vs 1/T, where INHB refers to the high‐frequency nonhydrogen‐bonded Gaussian component intensity (the shoulder), and IHB refers to the low‐frequency hydrogen‐bonded intensity (the peak), were charac...

Raman and Infrared Spectral Investigations of Water Structure

The models that have been proposed to represent the structure of liquid water are too numerous to be described here, but they are discussed in Chapter 14. Two general classes of models of interest for present purposes are usually designated by the terms continuum(1132) and mixture.(356) Continuum models treat water in terms of a continuous distribution of interactions that are presumed to be spectroscopically indistinguishable, whereas mixture models generally relate distinct spectral features to structures differing in the extent of hydrogen bonding. Some of the earlier spectroscopic investigations(1132) appeared to favor continuum models, but recent laser- Raman investigations(1138) as well as results from nonlinear optical techniques such as stimulated Raman scattering and hyper-Raman or inelastic harmonic light scattering strongly favor mixture models, e.g., the consecutive hydrogen-bond disruption model.

Raman and Infrared Spectral Studies of Aqueous Calcium Nitrate Solutions

Extensive Raman and infrared spectral data have been obtained from studies of aqueous solutions of Ca(NO3)2, as well as from mixtures involving high Ca2+–NO3− or NO3−–Ca2+ concentration ratios. The removal of the degeneracy of the E′ modes, even in dilute solution, and the activity of the A′ mode in the infrared spectrum suggest that the symmetry of the nitrate ion has been lowered by solvation with water. The perturbation is enhanced by ionic interaction with hydrated calcium ions. The implications of the model are discussed.