Spectrum of the velocity autocorrelation function of a molecule in a liquid

The theory of the autocorrelation function _V(t) of the velocity of an isolated molecule is formulated, taking into account the contributions of longitudinal and transverse modes of motion. The spectral density function of _V(t) accordingly, turns out to be expressed in terms of two independent susceptibilities, one of the relaxation type and the other of the wave type. The simple dispersion model constructed on the basis of the theory developed in the article agrees very precisely with the data of a computer experiment for liquid argon over the entire range of variation of.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 27–32, August, 1978.