Raman Spectroscopic Study on the Temperature Dependence of the Uncoupled O–D Stretching Band from HDO Molecules in Concentrated Aqueous Zn(ClO4)2 Solutions

Polarized Raman spectra of the uncoupled O–D stretching vibrational bands in concentrated aqueous Zn(ClO4)2 solutions have been recorded in the temperature range of 26—95 °C. Observed isotropic and anisotropic spectra have been analyzed by a double-difference method, in conjunction with a least squares fitting procedure, to deduce Raman band components arisen by HDO molecules in the first hydration shell of the constituent ions in the solution. Two band components centered near 2420 and 2640 cm−1 were assigned to the O–D stretching vibrational mode of HDO molecules coordinated to Zn2+ and ClO4−, respectively. These frequencies agree with the infrared double-difference results. Further, it has been found that the relative integrated intensity of the ion-perturbed O–D bands is quite different from that of the ‘bulk’ HDO molecules. The temperature dependence of peak parameters such as the frequency and peak area for Zn2+ and ClO4−-perturbed bands is very small in the temperature range of 26—95 °C, in contrast to a pronounced collapse of the band from bulk HDO molecules at elevated temperatures. This suggests that the local structure around these ions in the solution changes little in the temperature range examined in this study.