Camille Chapados

Isotope effects in liquid water by infrared spectroscopy. III. H2O and D2O spectra from 6000to0cm−1

The infrared spectra (IR) of pure liquid light (H(2)O) and heavy (D(2)O) water were obtained with attenuated total reflection (ATR) and transmission measurements in the mid-IR and far-IR. With these and with other values obtained from the literature, the real (n) and imaginary parts (k) of the refractive index were meticulously derived in the complete IR region from 6000 to 0 cm(-1). The reliability of the results resides in the critical comparison of our experimental data with that obtained from other laboratories and between calculated and experimental spectra, obtained by ATR and transmission techniques. The new optical properties (n and k) can now be used as standards for liquid H(2)O and D(2)O. To these we have added the water (H and D) absorption coefficients (K) that are derived from the k values. These can be used as references for spectra obtained by transmission with an absorbance intensity scale because they are almost the same.

Isotope effects in liquid water by infrared spectroscopy

The light and heavy liquid water (H2O–D2O) mixtures in the 0–1 molar fraction were studied in the mid-infrared by Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. Five principal factors were retrieved by factor analysis (FA). When D2O is mixed with H2O, the HDO formed because of the hopping nature of the proton (H or D) results in three types of molecules in equilibrium. Because of the nearest-neighbor interactions, the three molecules give rise to nine species. Some of the species evolve concomitantly with other species giving the five principal factors observed. We present the spectra of these factors with their abundances. The calculated probability of the species present at different molar fractions which when the concomitant species are combined gives the observed abundances. To appreciate clearly the difference between the principal spectra, a Gaussian simulation of the bands was made. Because of the numerous components that make up the stretch bands, they are not ver...

IR spectroscopy of aqueous alkali halide solutions: Pure salt-solvated water spectra and hydration numbers

Extrapolation techniques were used to obtain pure salt-solvated water spectra from the attenuated total reflection infrared spectra (ATR-IR) of aqueous solutions of the nine alkali halide salts LiCl, NaCl, KCl, CsCl, NaBr, KBr, NaI, KI, and CsI and the alkaline–earth chloride salt MgCl2. These salts ionize completely in water. The ions by themselves do not absorb in the IR, but their interactions with water can be observed and analyzed. A pure salt-solvated water spectrum is easier to analyze than that of a combined solution of pure water and salt-solvated water. Although the salt-solvated water spectra examined have distinctive signatures, they can be classified in three categories: those similar to NaCl; those not similar to NaCl; and MgCl2, in a class by itself. Each of the pure salt-solvated water spectra differs from that of liquid water, though the number of bands is the same. From the Gaussian band fitting, we found that the positions of the bands were fairly constant, whereas their intensities dif...

Subtraction of the Water Spectra from the Infrared Spectrum of Saline Solutions

The infrared (IR) spectrum of a sample in a saline solution cannot be retrieved adequately when the spectrum of pure water is subtracted. Some water bands remain in the spectrum. The retrieved spectrum is good only when the spectrum of NaCl in water at the right concentration is subtracted. However, when the concentration of the salt is unknown, it is still possible to obtain a good spectrum of the sample free of water. This is done by subtracting from the original spectrum a fraction of two eigenspectra of water: one for pure water and one for NaCl solvated water. The fraction of the eigenspectra is determined with the 2100 and 3300 cm−1 bands. The effectiveness of the method is illustrated with a solution of sodium monochloroacetate in a saline solution.

Influence of Anomalous Dispersion on the ATR Spectra of Aqueous Solutions

Transmission spectra of aqueous solutions are difficult to obtain because in the 3 μm infrared region, the high absorptivity of water requires the use of thin films. In contrast, attenuated total reflectance (ATR) spectra of aqueous solutions, not requiring thin films, are easily obtained. Unfortunately, compared to measurements made by transmission, ATR measurements cause some variation in the band shape due to the anomalous dispersion (AD) effect. To evaluate these variations, we studied pure water and KCl aqueous solutions. We then compared the ATR spectra of both substances with the real and imaginary refractive index spectra calculated by using the Kramers–Krönig relation. As long as the proper material is used in the ATR cell and the concentration of water is not significantly decreased, then the IR-ATR measurements directly reflect the chemistry of the sample.

Infrared Titration of Aqueous Glycine

The infrared (IR) spectra of glycine in aqueous solutions were obtained in the pH range 0.2 to 14 in order to determine the ionic distribution of the molecule as a function of pH by factor analysis (FA). After subtraction of the water bands, FA was used to separate the spectra of each ionic species and determine their real abundance. The pKa values were retrieved from the volumetric titration as a function of pH and were used to obtain the theoretical abundance of each ionic species as a function of pH. These distribution curves were compared with the distribution curves obtained from IR. The agreement between the two curves was good. The following species were observed for glycine in water: the cation (pH 0 to 5); the zwitterion (pH 0 to 12.5); and the anion (pH 7 to 14).

SUBTRACTION OF THE WATER SPECTRA FROM INFRARED SPECTRA OF ACIDIC AND ALKALINE SOLUTIONS

The IR spectrum of a sample in acidic and alkaline solutions cannot be retrieved adequately when only the spectrum of pure water is subtracted. After such an operation, some water bands remain in the spectrum, which also has a distorted baseline. An analysis of a series of IR spectra of HCl and NaOH solutions showed that they could be represented by two pairs of eigenspectra, one pair for the acidic solutions and the other for the basic solutions. The fraction of each eigenspectrum of a sample in an acidic or alkaline solution is determined with the 2100 and 3300 cm−1 water bands. After subtraction, no baseline adjustment is necessary. The effectiveness of the method used to subtract the water bands is illustrated with solutions of malic acid at low and high pH.

Infrared absorption of SF6 from 32 to 3000 cm−1 in the gaseous and liquid states

Abstract Infrared spectra from 32 to 3000 cm −1 of SF 6 were recorded at several pressures, from below atmospheric pressure up to 20 atm and in the liquid phase at temperatures from 228 to 284 K. The infrared active fundamentals, difference bands, combination and harmonic bands, and the collision-induced band in the far-infrared region were observed. Integrated intensities of 37 bands were measured at several densities. In the gas phase, a weak band containing ν 2 + ν 6 was always found at higher frequencies than the much stronger bands containing ν 3 . In the liquid phase, the positions of these bands are lowered in frequency and the intensities tend toward equalization. The pair ν 3 and ν 2 + ν 6 itself is the exception: while the ν 3 band is displaced and its intensity lowered, the ν 2 + ν 6 band is practically not modified. A possible explanation of the modification in the intensity of the bands in passing from the gas to the liquid is the effect of the interaction with the liquid environment on the Fermi resonance connecting ν 3 and ν 2 + ν 6 . Within experimental error no collision-induced component was identified in the mid-infrared region in the gas phase. In the liquid phase, the integrated absorption of the bands increases with temperature, surpassing in many cases the gas-phase values.

Infrared spectroscopy of acetone–water liquid mixtures. I. Factor analysis

Acetone and water mixtures covering the whole solubility range were measured by Fourier transform infrared attenuated total reflectance spectroscopy. In this system, only water can supply the hydrogen atoms necessary for hydrogen bonding. Using spectral windowing with factor analysis (FA), 10 principal factors were retrieved, five water and five acetone. Hydrogen bonding is observed on the carbonyl stretch band as water is introduced in the solution, redshifting the band further from its gas position than that observed in pure liquid acetone. This indicates that the hydrogen bonding is stronger than the acetone dipole–dipole interactions because it overrides them. A water molecule isolated in acetone is twice H bonded through its two H atoms; although both OH groups are H-bond donors, the OH stretch band is less redshifted (∼138 cm−1) than that of pure liquid water (∼401 cm−1). This is attributable to the two lone electron pairs remaining on the oxygen atom that sustain a large part of the OH valence bond...

Interpolation and Extrapolation of Infrared Spectra of Binary Ionic Aqueous Solutions

Factor analysis of the attenuated total reflection (ATR) absorbance spectra of aqueous saline solutions has shown that these spectra are linear combinations of two eigenspectra: pure water and salt-solvated water. This paper outlines the general equations needed to formalize these experimental results. In the case of binary salts in aqueous solutions, the equations allow interpolation and extrapolation from one concentration to another. The accuracy of the calculation method was adequately verified on aqueous solutions of KCl. The equations made it possible to calculate the ATR absorbance spectrum of a “pure” KCl-solvated water. The latter, which contains no ordinary water, enabled us to determine that solvated water forms clusters made up of a pair of ions with five molecules of water. The same results were obtained with NaCl aqueous solutions.