Neutron-Diffraction Determination of the Crystal Structure and Magnetic Form Factor of γ -Oxygen

Single-crystal neutron-diffraction data have been used to refine the crystal structure of the paramagnetic cubic γ phase of oxygen at 46 ^∘{}K. Two of the eight molecules in the Pm3n unit cell are randomly oriented along the $〈111〉$ axes at the $2(a)$ positions, and the remaining six along the $〈100〉$ axes perpendicular to the fourfold inversion axes at the $6(d)$ positions. Associated with this disorder is a large librational motion with a rms amplitude of about 20^∘{}. Magnetic-form-factor values for 27 reflections have been measured by the polarized-neutron technique. Data were collected from large crystals subjected to an applied magnetic field of about 80 kOe in a specially designed split-coil superconducting magnet. The observed values are in good agreement with theoretical calculations described in the following paper based upon the usual molecular-orbital model with two unpaired electrons in the pπ antibonding orbitals.