High-resolution low-frequency Raman spectra of liquid H2O and D2O

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Abstract
New high-resolution experimental data on the low-frequency Raman spectrum of water and heavy water are presented. Both polarized and depolarized spectra are studied over a wide temperature range, including the supercooled liquid region. For the first time the absolute Raman cross section of the depolarized spectrum is reported to be ≊2×10−3 Å6/molecule, for both liquids within the experimental error at room temperature, and compared with the integrated intensity of the Brillouin doublet, 0.134 Å6/molecule. The analysis of the temperature behavior of both integrated intensity and line shapes, and the comparison with the results of molecular dynamics simulations indicate that the Raman spectra in the 0–50 cm−1 region are dominated by the dipole–induced dipole contribution. No direct evidence for H-bond polarizability modulations is found in this frequency region.