Structure of Liquid Oxygen by Neutron Diffraction

The angular distribution of 1.04 A neutrons scattered by specimens of liquid oxygen at 90.7°K, 69.0°K, 62.4°K, and 54.7°K has been measured over the angular range 3° to 78°. Pronounced excess scattering at low angles is taken to be magnetic in origin and its form suggests the possible existence of short range magnetic order in the liquid. The measured distributions corrected for magnetic scattering were transformed to the radial distribution functions $4\pi r^2\left[\rho \mathrm{}\right(r)-{\rho }_0]$. An analysis of these gives ${1.2}_6$ atoms and 1.26 A as the number of neighbors in, and the spacing of the diatomic shell, 2.7 A as the nearest distance of approach of 2 atoms in adjacent molecules in the liquid and about 3.9 A as the spacing of the main density maximum. The total number of atoms in the main density maximum increases from about 16 to 21 atoms for temperature change from 90.7°K to 54.7°K. The possible existence of the ${\mathrm{O}}_4$ molecule is discussed.