This paper demonstrates that characteristics of low-energy excitations in water observed in Raman scattering and inelastic neutron and x-ray scattering experiments follow naturally from a simple-model analysis, taking into account essential features of water structure in the center-of-mass system. It is shown that the modes associated with the lower band near $60{\mathrm{cm}}^{-1\mathrm{}}$ are strongly localized with localization lengths of the order of their wavelength and the higher band near $180{\mathrm{cm}}^{-1\mathrm{}}$ attributes to mesoscopically localized modes within the network connected by hydrogen bonds.

• Received 13 August 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.1244