MICROSCOPIC STRUCTURE OF THE HYDROGEN-XENON MIXTURE

We report a neutron-diffraction study of the microscopic structure of the H-2-Xe binary mixture in the Xe-rich phase, x(Xe)=0.78, at T=283 K and P=170 bars, i.e., in the vicinity of the second-type gas-gas demi xing surface. The site-site distribution functions are extracted emplo ying the H-D isotopic substitution technique. We report also molecular -dynamics simulations for a mixture of equivalent Lennard-Jones (LJ) a toms. The experimental results are compared with previous ones obtaine d for the He-Xe and Ne-Xe mixtures, which show a first- and a second-t ype gas-gas transition, respectively. The general picture already sugg ested by the other two mixtures agrees also with the present results, although in this case the center-center distribution functions H-2-H-2 and H-2-Xe are clearly modulated by the Xe-Xe correlations. In partic ular the features found in the distribution functions of the mixture s uggest that the LJ potential model is not able to reproduce at a satis factory level the H-2-H-2 and the H-2-Xe correlation functions and tha t a (XeH4) chemical complex is present.