Structure and forces in expanded liquid cesium

Abstract

The paper presents a neutron diffraction investigation of the static structure factor S(Q) of liquid cesium expanded by heating toward conditions close to its liquid-vapor critical point. The experiment was designed to obtain the isothermal density derivative of S(Q) which is related to the triplet correlation function. The data give the first information on the density-dependent changes in the interatomic forces as the metal-nonmetal transition is approached in the expanded liquid. In particular, the results provide direct experimental evidence for the limitation of the uniform fluid model.

Structure of Liquid Rubidium and Liquid Sodium under Pressure.

“…The height of the first peak of S(Q) increases with increasing pressure. With increasing temperature at constant pressure, the peak height is known to decrease [6,7]. In the present measurements along the melting curve, the peak height increases with pressure in spite of increasing temperature, indicating that the structure of liquid becomes higher packing structure with compression.…”

“…With increasing pressure the peak position rl of the first-peak shifts to shorter distance. As shown [6] and fluid Cs [7] for reference. Results for liquid Cs [8] are shown for comparison .…”

Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for pure liquids

“…For simple liquids, it has already been shown that this type of integral is useful. 8,9,13,14,22,49,55,[58][59][60][61][62] Using FST, integrals over g (3) α βγ and g (4) α βγδ may now be obtained without the need for scattering experiments, albeit with a loss of spatial resolution. They may be obtained for any liquid (or solution) where the required bulk thermodynamic data have been determined.…”

“…Nevertheless, the integral has been useful for the few systems for which the rdfs are obtainable. These relationships, first provided by Buff and coworkers and by Schofield,22,[58][59][60][61] have been used extensively by Egelstaff and others to test theories and models for g (3) α βγ 8,9,13,14,22,49,55,[58][59][60][61][62] and are described below. Our work is similar to the S(Q → 0) limit of Egelstaff's (and others') work, which is focused on S(Q) and therefore only technically valid for monatomic liquids.…”

“…8 Gläser and coworkers presented a neutron diffraction investigation of the S(Q) of liquid cesium close to its liquid-vapor critical point to obtain the isothermal density derivative of S(Q). 62 Soper and coworkers measured the isothermal density derivative of S(Q) of dense fluid helium by neutron diffraction to test a model for g (3) . 55 Finally, Egelstaff 64 additionally assessed the second derivative of S(Q) with respect to pressure for liquid neon at 35 K and ρ = 1.119 g/cm 3 , which is related to integrals over the quadruplet correlation function, and Ballentine 65 has further considered the long wavelength limit.…”