The previously reported nonreproducibility of the intensity of the OH stretching band of liquid water has been explored. It was found that it can be eliminated in measurements with the Circle® multiple ATR cell by ensuring that the ATR rod is coaxial with the glass liquid holder. It was also found that normal laboratory temperature variations of a few degrees change the intensity by ⩽∼1% of the peak height. A new imaginary refractive index spectrum of water has been determined between 4000 and 700 cm1 as the average of spectra calculated from ATR spectra recorded by four workers in our laboratory over the past seven years. It was obtained under experimental and computational conditions superior to those used previously, but is only marginally different from the spectra reported in 1989. In particular, the integrated intensities of the fundamentals are not changed significantly from those reported in 1989. The available imaginary refractive index, k, values between 15,000 and 1 cm−1 have been compared. The values that are judged to be the most reliable have been combined into a recommended k spectrum of H2O(l) at 25 °C between 15,000 and 1 cm−1, from which the real refractive index spectrum has been calculated by Kramers–Kronig transformation. The recommended values of the real and imaginary refractive indices and molar absorption coefficients of liquid water at 25 ± 1 °C are presented in graphs and tables. The real and imaginary dielectric constants and the real and imaginary molar polarizabilities in this wavenumber range can be calculated from the tables. Conservatively estimated probable errors of the recommended k values are given. The precision with which the values can be measured in one laboratory and the relative errors between regions are, of course, far smaller than these probable errors. The recommended k values should be of considerable value as interim standard intensities of liquid water, which will facilitate the transfer of intensities between laboratories.

We have recorded multiple attenuated total reflection spectra of liquid H20 and D20, using the Spectra-Tech CIRCLE cell, and calculated from them the infrared optical and dielectric constants and molar conductivities from 9000 to 1250 cm"1 for H20 and from 8500 to 700 cm"1 for D20. Our results agree well with the literature for H20, while our results for D20 are the most extensive reported to date. We have calculated the dipole moment derivatives with respect to stretching and bending internal coordinates from the areas under the bands in our molar conductivity spectra. For lack of information, we have used the assumptions of the simple bond-moment model, a diagonal force field, and neglect of stretch-bend interaction.We found µ/dr for the stretching vibrations to be 3.02 D/Á ±1% and 3.04 D/Á ±0.5% for H20 and D20, respectively, and µ/ for the bending vibration to be 0.73 D ±3% for HzO and 0.63 D ±5% for D20. The two values for the stretching vibrations are indistinguishable, but this is not true for the bend. The disagreement for the bending vibration is probably due, at least in part, to our simulation of the absorption by three distinct bands of mixed Gauss-Lorentzian character, in order to try to separate the bending mode from the background absorption. It is probable that no such separation exists precisely. The bond moments for H20 and D20 agree with those calculated by the same approximations from literature data for HDO to about the extent allowed by the approximations. The intensities for liquid H20 are compared with those for water in the gas phase, in Ba(C103)2-H20, in ice I, and in lithium ^-alumínate. The intensity of the bending mode, v2(H20), is essentially independent of the strength of the hydrogen bonds. That of the OH stretching modes increases with hydrogen bond strength in Ba(C103)2-H20, liquid water, ice I, and lithium ß-aluminate being 20, 17.5, 25, and 40, respectively, times more intense than in the gas. Explanations for this are briefly summarized.

The real and imaginary refractive index spectra of mixtures of water and acetonitrile over the full composition range at 25 °C were determined between 8000 and 700 cm-1 by calibrated multiple attenuated total reflection spectroscopy. Under the assumption of the Lorentz local field, the corresponding molar polarizability spectra, αm(ν̃) = α‘m(ν̃) + iα‘‘m(ν̃), were calculated and used to investigate the structure of the mixtures. The concentrations of water-bonded, acetonitrile-bonded, and non-hydrogen-bonded O−H groups, and of water-bonded and non-hydrogen-bonded acetonitrile molecules, were obtained from the integrated intensities C OH and C CN, the areas under the O−H and C⋮N stretching bands in the ν̃α‘‘m spectra. The results indicate that no enhancement of the water structure (OH---O bonding) results from the addition of acetonitrile. In contrast, a monotonic decrease in the fraction of O−H groups that are bonded to oxygen is observed with increasing CH3CN content. At low acetonitrile concentration, x CH 3 CN ≤ 0.05, where x is the mole fraction, the total fraction of OH groups that are hydrogen bonded increases slightly with increasing CH3CN content because the formation of OH---N bonds slightly exceeds the destruction of OH---O bonds. The present results are consistent with the existence of microheterogeneity at compositions near 30−50 mol % of acetonitrile. However the fraction of OH groups that are hydrogen bonded to water is 0.50 at 50 mol % CH3CN and decreases to 0.35 at 70 mol % CH3CN. Both of these fractions are too small to support water clusters more complex than linear chains or hexagons

Articles you may be interested inThe infrared spectrum of ice IV in the range 4000-400 cm−1 J. Chem. Phys. 71, 4050 (1979); 10.1063/1.438173Optical spectra of orientationally disordered crystal. V. Raman spectrum of ice Ih in the range 4000-350 cm−1 P 0 SIT RON I U M C HEM 1ST R YIN A QUE 0 U S K M n 0 4 SOL UTI 0 N S 4501 identification card and a control card. The control card contains the value of the intercept (A) at point P, the decay constant >' 2, the background counts, and the number X whose value is relative to the point P=O. The program now reads data points from point B to (X-1) and performs background subtraction. THE JOURNAL OF CHEMICAL PHYSICSThe data points from the least-squares curve XD are now read in and compared point by point with curve PD until the point D is determined. The program now proceeds to find Area 1, Area 2, Area 3, and the intensity 12• The results are printed out and the program proceeds to the next data set.The absorbance of several samples of ice Ih has been measured in the range 4000-30 em-I, and scaled to that of a particular film of unknown thickness. The thickness of the film has been calculated by two methods, first from the known absorptivity at 4940 em-I, and second by equating the appropriate Kramers-Kronig integral to the known infrared contribution to the microwave refractive index. The two thicknesses agreed well and allowed the absorptivity to be obtained in the range 4000-30 em-I. The complex refractive index and permittivity and the normal incidence reflectivity have been calculated from the absorptivity. About three-quarters of the infrared contribution to the microwave refractive index is caused by the translational lattice vibrations and about 15% by the rotational vibrations; the o-H stretching bands which absorb very strongly contribute relatively little. The maximum of the density of states in the transverse acoustic branch is at 65 em-I rather than below 50 em-I as reported earlier. Below 50 cm-I the absorptivity is roughly proportional to the fourth power of the frequency. This arises because the vibrations here are short-wavelength sound waves with a density approximately proportional to the square of the frequency, and the integrated intensity of absorption by one vibration is proportional to the square of the frequency. A theory of the contribution of the translational lattice vibrations to the microwave permittivity is given based on the theory of the absorption by orientationally disordered crystals given in an earlier paper. From the theory and the experimental measurements reported in this paper the dipole-moment derivative for the relative displacement of two water molecules in ice along their line of centers (or equivalently the effective charge of a water molecule) is about 0.3 electronic charges.

The infrared spectra of Ice Ih made from H2O, D2O, a mixture of 95% H2O and 5% D2O, and a mixture of 5% H2O and 95% D2O, and of Ice Ic made from H2O, D2O, and a mixture of 95% H2O and 5% D2O, have been recorded in the region 4000 to 350 cm—1 using low-temperature mulling techniques developed in these laboratories. The Ice Ic was made by transformation of Ices II and III, and was authenticated by its x-ray diffraction powder pattern. The spectra of Ices Ih and Ic are identical within experimental error. The spectra of Ice Ih, while similar in their main features to those reported by earlier workers, differ significantly in detail, probably largely because much of the previous work, particularly on D2O ice, has been done with partly vitreous ice. The usual interpretation of the bands in terms of the v1, v2, v3, and vR vibrations of isolated molecules is greatly oversimplified because intermolecular coupling is important. There are at least six (five infrared and one Raman) bands due to O—D stretching vibrations in the spectrum of D2O Ice I, but the detailed origin is unknown. The breadth of the O–H and O—D stretching bands of HDO in dilute solution in D2O and H2O is interpreted as indicating a disarrangement of the oxygen positions due to the disorder of the hydrogen atoms.