Polarized Raman spectra for the full range of isotopic dilution for ice Ic and amorphous ice: Mixtures of intact H2O and D2O

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Abstract
The 90 K polarized Raman scattering of thin films of ice Ic and ice Ia containing mixtures of intact H2O and D2O have been measured using the interference‐enhanced internal‐reflection technique. The effects of isotopic dilution reported for samples with a D2O content ranging from 0% to 100% are consistent with the commonly held view that intermolecular coupling produces collective vibrational modes that determine the appearance of the Raman spectra in the stretching mode region of crystalline and amorphous ice. The convergence of bands produced by the collective modes on the isotopically decoupled mode frequencies of both ν1 and ν3 is displayed in this study. Bands at 3323 and 3209 cm−1 in the anisotropic scattering of protiated ice Ic are shown to converge on the decoupled antisymmetric stretch frequency of 3370 cm−1. The gradual shift of the dominant isotropic scattering at 3085 cm−1 towards the frequency of the decoupled ν1 mode is also revealed, with bands for the first stage in the evolution of the in‐phase ν1 collective mode, i.e., the neighbor coupled mode, observed at 3180 (H2O) and 2340 cm−1 (D2O). The data also suggest that the shift of the in‐phase coupled ν1 band begins with the first traces of added diluent, a behavior that indicates a macroscopic extension of the resonant coupling for both crystalline and amorphous ice. By contrast, the insensitivity of isotropic scattering near 3420 cm−1 to isotopic dilution suggests that the overtone of the bending mode is the likely source.