Evidence for the importance of intermolecular coupling in the OD band's vibrational structure in deeply supercooled liquid D2O

We present the Raman spectrum of pure liquid D₂O at −27.0°C, 17°C lower than any previously reported Raman spectrum of liquid D₂O. The liquid's OD stretch band at −27.0°C displays a prominent feature which is clearly analogous to the ν₁ in-phase mode in D₂O ice Ih providing strong evidence that the structure of cold liquid D₂O's OD band is principally due to strong intermolecular coupling. Deeply supercooled liquid D₂O displays this ν₁ in-phase feature more clearly than deeply supercooled liquid H₂O due to the smaller disparity in the D/O mass ratio compared to that of H/O which enhances this coupling.