Interpretation of IR and Raman line shapes for H2O and D2O ice Ih.

Noticeable differences between the vibrational (IR and Raman) spectra of neat H(2)O and D(2)O ice Ih are observed experimentally. Here, we employ our theoretical mixed quantum/classical approach to investigate these differences. We find reasonable agreement between calculated and experimental line shapes at both high and low temperatures. From understanding the structure of ice Ih and its vibrational exciton Hamiltonian, we provide assignments of the IR and Raman spectral features for both H(2)O and D(2)O ice Ih. We find that in H(2)O ice these features are due to strong and weak intermolecular coupling, not to intramolecular coupling. The differences between H(2)O and D(2)O ice spectra are attributed to the significantly stronger intramolecular coupling in D(2)O ice. Our conclusion for both H(2)O and D(2)O ice is that the molecular symmetric and antisymmetric normal modes do not form a useful basis for understanding OH or OD stretch spectroscopy.