LOW-FREQUENCY DEPOLARIZED RAMAN-SPECTRA IN WATER - RESULTS FROM NORMAL-MODE ANALYSIS

The Raman spectrum of water in the translational frequency regime has been interpreted in terms of localized vibrational density of states and, in seeming contradiction, in terms of contributions of long-range dipole induced dipole (DID) reactions. We show that these interpretations can be consistently understood by obtaining the Raman spectrum from the normal modes of the inherent liquid structures. We calculate the DID contributions to the Raman spectra for each individual mode, and show that the aggregate spectrum obtained agrees well with both the DID spectrum obtained directly from a molecular dynamics simulation and the spectrum obtained by simulating harmonic dynamics (i.e., exciting all the modes at once and calculating the DID spectrum from the resulting dynamical trajectory of the system).