2-BODY AND 3-BODY LONG-RANGE FORCES IN ARGON AND XENON BY MEANS OF SANS

The long-range interaction in fluids is dominated by the attractive pa ir contribution U-2; nevertheless it is well known and experimentally demonstrated that an accurate investigation requires the inclusion of the three-body contribution U-3 even in the low-density regime. The ch aracterization of both U-2 and U-3 is usually obtained by means of sem iempirical methods, the only exception being presently represented by SANS experiments on rare gases fluids. In this case the knowledge of S (k) in the low k-range allows a direct experimental determination of t he U-2 and U-3 intensities, namely C-6 and v. We report here the resul ts of SANS experiments on low-density Ar and Xe performed at the PAXE diffractometer (LLB, Saclay). The effects of three-body forces are cle arly separated from the pair contribution: the first experimental dete rmination of C-6 and v in those systems has been obtained, showing goo d agreement with the corresponding values found in literature. (C) 199 8 Elsevier Science B.V. All rights reserved.