RAMAN-SPECTROSCOPIC EVIDENCE FOR INCREASING CONTACT ION-PAIRING IN THE GLASSY STATES OF DILUTE AQUEOUS CALCIUM NITRATE SOLUTIONS

Raman spectra of aqueous solutions of approximate to 0.5 and approximate to 0.05 M calcium nitrate recorded in their glassy states at 90 K are reported and compared with those recorded at 295 K. Evidence for increasing contact-ion pairing in the glassy state is based on increasing intensity of a band in the upsilon(4) band region at approximate to 740 cm(-1). In the upsilon(1) band region two peaks can be resolved, with maxima at approximate to 1049 cm(-1) for the contact-ion pair and at approximate to 1036 cm(-1) for ''free'' nitrate. Relative intensities of bands due to ''free'' nitrate and contact-ion pair were determined by curve fitting the upsilon(4) and upsilon(1), band region. This curve fitting analysis shows that in the glassy state the molar intensities of ''free'' and contact-ion-paired nitrate cannot be equal in both spectral regions.