Elementary Excitations in Classical Liquids

Abstract

Collective dynamical variables in classical liquids, having the character of longitudinal and transverse phonons, are proposed. A variational argument is used to determine their frequency spectrum; the sound velocities of long-wavelength modes are determined by elastic moduli of the liquid. Their lifetimes are estimated, and turn out to be of the order of ${10}^{-13\mathrm{}}$ sec for normal liquids, but much longer for highly viscous liquids (glasses).