Single-particle kinetic energies in liquid neon.

Abstract

High-energy neutron-scattering experiments are reported on three samples of liquid natural neon. One was at 25.8 K at low pressure and two near 35 K were pressurized to densities differing by 9%. Measurements were made at wave-vector transfers Q in the range 200--280 ${\mathrm{nm}}^{\mathrm{\ensuremath{-}}1}$, within the impulse approximation, with accounting for spectrometer resolution and multiple-scattering effects. Single-particle kinetic energies, 〈${\mathit{E}}_{\mathit{k}}$〉, were determined by assuming a Gaussian atomic momentum distribution. The value 〈${\mathit{E}}_{\mathit{k}}$〉/${\mathit{k}}_{\mathit{B}}$=52.8\ifmmode\pm\else\textpm\fi{}3.7 K at 25.8 K is found to be somewhat larger than a deduction in the literature from experimental work at Q values below 100 ${\mathrm{nm}}^{\mathrm{\ensuremath{-}}1}$. The difference between current measurements and the previous deduction can be attributed to the failure of previous measurements to operate within the impulse approximation. Our two values of 〈${\mathit{E}}_{\mathit{k}}$〉 near 35 K differ by (4\ifmmode\pm\else\textpm\fi{}0.3)%, a small relative difference. A comparison of the present results for 〈${\mathit{E}}_{\mathit{k}}$〉 with calculated values dependent upon S(Q) measurements (and inferred pair-correlation functions) shows only qualitative agreement, as does a comparison with a published Wigner-Kirkwood expansion of the density matrix, using a Lennard-Jones potential.