Vibrational Spectra of Molten Salts. I. Infrared Spectra of Calcium Nitrate in Alkali-Metal Nitrate Solutions

Infrared spectra of thin films of Ca(NO3)2 dissolved in molten KNO3 and molten NaNO3 have been obtained over the spectral range 4000–200 cm−1. The changing appearance of the spectra as a function of calcium content indicates clearly an asymmetric perturbation of the nitrate ion by the calcium ion in these mixtures. The magnitude of the perturbation is, however, similar to that found in concentrated aqueous calcium nitrate solutions, consistent with the existence, in both types of systems, of contact ion pair complexes. A new band at 332 cm−1 in the spectra of melts containing Ca2+ characterizes the Ca–ONO2 stretching frequency. Addition of chloride ion in the form of KCl to KNO3/Ca(NO3)2 molten mixtures was found to restore the appearance of the spectrum towards that of pure KNO3, showing that Cl− ion displaced NO3− from the Ca2+–ONO2− complexes.