Structure of Liquid Nitrogen, Oxygen, and Argon by Neutron Diffraction

Abstract

The structures of liquid oxygen, nitrogen, and argon have been investigated by measuring the scattering of neutrons of wavelength 1.08A over the angular range 4\ifmmode^\circ\else\textdegree\fi{} to 78\ifmmode^\circ\else\textdegree\fi{}. The scattering curves have been transformed to give the time average of the atomic density as a function of the distance from an atom taken as center. The deviation from the mean density is an oscillating function with an amplitude which decreases more rapidly than the inverse square of the distance from the central atom. In nitrogen a single neighbor is found at a spacing of 1.1A from each atom, corresponding to a diatomic molecule in the liquid. In oxygen 1.5 neighbors are found at approximately 1.25A from each atom, suggesting that the degree of association is greater than diatomic. The results are not inconsistent with the suggested existence of the ${\mathrm{O}}_{4}$ molecule. In argon the results are in reasonable agreement with published x-ray determinations.