Spectrum Of Pure Water Research Articles

Interpretation of the Raman spectra of aqueous acid solutions in terms of the polarizability of hydrogen bonds. Part 1.—Aqueous HCl solutions

In the Raman spectra of pure water and aqueous HCl solutions a continuous scattering is found, similar to the continuous absorption observed with the i.r. spectra of acid solutions. The continuum of energy level differences probably arises from the extremely large proton polarisability of the hydrogen bond in the H5O+2 grouping, since the large polarisability causes interaction effects of these hydrogen bonds with their environment, so shifting the energy levels. Below 300 cm–1 an extremely strong intensity increase for the acid solution is caused by the O ⋯ O stretching vibration. One reason for this Raman intensity may be the large change of the hydrogen bond polarisability caused by the proton as a function of the O ⋯ O distance in the hydrogen bond (OH ⋯ O)+. The intensity of the H2O torsional vibrations at 780 and 450 cm–1 rises, too, with increasing acid concentration, but not as strongly. This, also, may be explained by the large proton polarisability of the H-bond.

Far-Infrared Absorption Spectra of Aqueous Solutions of Strong Electrolytes

The infrared absorption of solutions of LiCl, KF, KCl, KBr, KI, NaCl, NaBr, NaI, NaNO3, NaClO3, DCl, and NaOD in NaClO4 has been studied in the spectral region 75 to 650 D2O; the absorption of HCl and NaOH solutions in H2O in the region 75 to 1000 cm−1 has also been investigated. Even for the highest concentrations, the solution spectra have a striking resemblance to the spectrum of the solvent. A broad, intense band attributable to the hindered rotation of water molecules and a much less intense band attributable to the hindered translation of water molecules appear in the spectrum of each solution. The frequencies, widths, and shapes of these bands are compared in some detail with the corresponding bands in the spectrum of pure water. Small but significant differences between the spectra of the solutions and the spectrum of water are noted.

Polarisation of the Raman Spectrum of Water

THE Raman spectrum of water has been studied in great detail by a large number of workers, notably A. S. Ganesan and S. Venkateswaran and A. L. Meyer. So far as I am aware, however, no attempt seems to have been made to study the polarisation of the Raman bands. I have studied the Raman spectrum of pure water by the original method of Raman. The liquid, which was enclosed in a large bulb, had been carefully purified by repeated distillation in vacuo. The polarisation photographs of the liquid were taken with a fairly wide slit, due corrections in the exposures for the two directions of the nicol, for the polarisation introduced by the optical train in the glass spectrograph itself, having been made by a previous calibration of the instrument.

Scientific Serials

Wiedemann's Annalen der Physik und Chemie, No. 7—Absorption spectrum of pure water for red and infra-red rays, by E. Aschkinass. The “extinction coefficients” of water for the various wave-lengths at the red end of the spectrum were determined by the bolometer, and calculated by the formula