Four-photon polarization spectroscopy of D2O intermolecular vibrations

For the first time, the spectra of heavy water in solid and liquid states in the frequency range 0-50 cm -1 are measured and systematically studied using polarization-sensitive four-photon spectroscopy. It is demonstrated that the frequencies of the resonances observed agree well with the frequencies of cooperative and intermolecular vibrations calculated earlier. The coincidence of the resonance frequencies for the liquid and solid phases gives evidence of the hexagonal structure of molecular clusters in the liquid phase and their relative stability. The same feature of the molecular clusters in liquid water is proved by the results of low-frequency spectroscopy of an equimolar mixture of heavy and light water, which was obtained for the first time.