The Raman spectra of aqueous and crystalline sodium iodate, iodic acid, and deuterioiodic acid have been recorded. The vibrational assignment for the 1 0 3 -ion has been revised, and eight of the nine fundamental vibrations of iodic acid have been assigned. Osmotic and activity coefficients of aqueous solutions of iodic acid and sodium iodate have also been measured, and an ionization constant of 0.18 f 0.01 has been calculated from a combination of these data with the degree of ionization as determined from Raman measurements. This value is somewhat higher than those which have been reported from conductance measurements.The Raman spectra of aqueous solutions of iodic acid and alkali metal iodates have been investigated by numerous workers.2 The measurements of the depolarization values of the Raman lines of the chlorate, bromate, and iodate ions were made by Shen, Yao, and W U .~ In their study, they used the sodium salts for the chlorate and bromate ions while a 6.1 N solution of iodic acid was used to study the Raman spectrum of the iodate ion. The strong line a t 806 cm.-' in the BrOa solution was quite symmetrical and assigned to v1 and the v3 fundamental was not observed. However, in the iodic acid solution the 779-cm.-' line was asymmetrical with a strong shoulder at 826 cm.-l. The shoulder was assigned as the vg fundamental of the pyramidal IO3ion. Although this assignment for the 1 0 3 -ion has been accepted by recent research w0rkers,~!5 there is a strong indication that this shoulder arises from a vibration of the undissociated HI03 molecule rather than from the IO3-ion.6 Therefore, a reinvestigation of the Raman spectra of aqueous solutions of both sodium iodate and iodic acid was undertaken.The Raman spectrum of crystalline Na1032* has been studied and four frequencies of approximately the same intensities in the range 737 to 808 cm.-l were reported. The Raman spectrum of crystalline iodic acid has also been studied2*v7,8 but the earlier work is incomplete and no vibrational analysis has been carried out. A comparison of the strong Raman lines of the crystalline iodic acid in the 1-0 stretching region with those reported as fundamentals in a recent infrared study4 shows a discrepancy between the frequencies chosen as fundamentals in the infrared and the strong Raman lines we observed. Thus, the Raman spectra of crystalline KaIo3, HO'IOz and DO'IO2 were investigated for the purpose of removing this discrepancy and giving a more complete vibrational assignment.Many values have been reported for the ionization constant of iodic acid and these are summarized in Table I.9-15 Most of them have resulted from meas-(1) Tennessee Eastman Fellow, 1964Fellow, -1965 (2) For a review of the early spectrographic literature, see (a) J. H.
The v2 + t>3 combination band of water has been recorded for bulk water and for very dilute solutions of water in various organic solvents. In each instance, the bands due to the organic solvent have been eliminated by placing a matched cell of pure solvent in the reference beam. This also served the purpose of cancelling any trace of moisture in the solvent before adding the measured quantity of water. This particular band was chosen because there is no interference from OH groups in hydroxylic solvents such as alcohols and glycols, and hydroxy or amido compounds of biological interest. The water band has been resolved by a computer program into three Gaussian components which have been identified with the 1:1 water-solvent and the 1:2 water-solvent complexes. The assignments have been verified by dilution of the complexes with CCI4 and CgHg. The positions of the bands and their widths at half-intensity vary in a predictable manner with the degree of hydrogen bonding and with the basicity of the solvent. The total areas under the curves are dependent, within experimental error, only on the amount of water present. Interactions between water and oxygen-containing organic solvents are strongest in DMSO of all solvents studied and weakest in nitromethane.
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