Correlation functions in classical gases at high frequency.
A general procedure is outlined to determine the exact asymptotic form of spectra in classical gases at high frequency. Examples are the force-force correlation or the velocity autocorrelation function of a tagged particle. For purely repulsive potentials of the form Ar(-n), the asymptotic spectra are proportional to omega(sigma)exp[-(omegatau)(nu)]. Exponent nu and time constant tau depend only on the interparticle potential, while exponent sigma depends in addition on the correlation studied. The analysis makes use of the fact that the high-frequency spectra are dominated by high-energy binary collisions. It is argued that for arbitrary potentials the spectra decay slower than exp(-constxomega(2/3)) and that the results are also relevant for dense fluids. The frequency range is estimated where quantum effects become important.
Teubner
Max
M
Max-Planck-Institut für Biophysikalische Chemie, Postfach 2841, 37077 Göttingen, Germany.