NEUTRON-DIFFRACTION OF LIQUID NEON AND XENON ALONG THE COEXISTENCE LINE

In this paper, we report neutron-diffraction measurements and molecular-dynamics simulations on liquid neon and liquid xenon for three thermodynamic states along the liquid branch of the coexistence curve. These states are the nearly orthobaric ones at 26.1, 36.4, and 42.2 K in the case of neon and at 169.0, 236.8, and 273.9 K for xenon. Apart from some general considerations on the density dependence of the liquid structure, one can point out that, first of all, contributions from quantum effects in the radial distribution function g(r) of liquid Ne are certainly lower than 2% for all the thermodynamic states studied. Secondly, a two-body additive interatomic potential, with parameters derived from gas-phase properties, cannot reproduce the experimental g (r) at least with an accuracy better than 5% for the height of the first peak and better than 1% for its position. Moreover, the many-body terms, which should be present in the interatomic potential, produce effects on g (r) which appear to be density independent, at least in the density range under study. These many-body terms are not adequately represented by a three-dipole Axilrod-Teller term.