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

Single-crystal neutron-diffraction data have been used to refine the crystal structure of the paramagnetic cubic $\gamma$ phase of oxygen at 46 °K. Two of the eight molecules in the $\mathrm{Pm}3n$ unit cell are randomly oriented along the $〈111〉$ axes at the $2\left(a\right)\mathrm{}$ positions, and the remaining six along the $〈100〉$ axes perpendicular to the fourfold inversion axes at the $6\left(d\right)\mathrm{}$ 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 $p\pi$ antibonding orbitals.