Collective oscillation in liquid water

Abstract

Measurements of the optical properties of liquid water were extended in the vacuum ultraviolet up to an energy of 25.6 eV. The indices of refraction and dielectric functions were obtained by a Kramers-Kronig analysis using reflectances measured in this study between 7.6 and 25.6 eV and reflectances from the literature below 7.6 eV. Our interpretation of the prominent peak in the energy loss function at about 21 eV is that it represents a collective electronic oscillation.