EXPERIMENTAL-DETERMINATION OF THE LONG-RANGE POTENTIAL OF ARGON PAIRSBY MEANS OF SMALL-ANGLE NEUTRON-DIFFRACTION

We have experimentally determined the static structure factor S(k) in low density argon gas for 1.0 < k < 3.5 nm(-1), by means of the small- angle neutron scattering diffractometer PAXE at Laboratoire Leon Brill ouin in Saclay. The experiment has bean performed at three number dens ities between 1.51 x 10(27) and 2.30 x 10(27) m(-3) along the T = 138. 75 K isotherm. From the data the small-k dependence of the Fourier tra nsform c(k) of the direct correlation function c(r) has been derived a nd the existence of the \k\(3) term in the behavior of c(k) experiment ally demonstrated. The experiment has allowed the first direct measure ment of the coefficient C-6 of the London dispersion interaction in th e pair potential of argon.