On the Pressure Dependence of the Structure in Liquid Neon and Sodium

Abstract

Recent neutron diffraction data for liquid neon and X-ray diffraction data for liquid sodium have been analyzed for the purpose of studying the pressure dependence of the structure in these liquids by means of the method proposed by Egelstaff, Page and Heard. In both cases, it was found that the function \ ildeH(Q), which expresses the deviation from the superposition approximation, is not zero, though the pressure derivative of the structure factor gives little contribution to the function \ ildeH(Q). Therefore, the superposition approximation is not necessarily sufficient for the description of the triplet correlation function in liquid neon and sodium.
Besides, the pair potentials have been calculated from these diffraction data at various pressures using the Born-Green equation. The pair potentials obtained for three states of liquid neon are of the Lennard-Jones type, whereas those obtained for liquid sodium with a provisional assumption based on the experimental results are of the long-range oscillatory type. The difference in the pressure dependence of the structure factor for liquid neon and sodium can be explained by the pair potential functions calculated in this work.