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

Abstract

Single-crystal neutron-diffraction data have been used to refine the crystal structure of the paramagnetic cubic y phase of oxy'gen at 46'K. Tvm of the eight molecules in the Pgm3n 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 follovring paper based upon the usual molecular-orbital model with two unpaired electrons in the pg antibonding orbitals.

The structure of N2 at 49 kbar and 299 K

“…05677408/81/01000804501.00 Schiferl, 1979), we made X-ray diffraction measurements on a single crystal of N 2 in a diamond cell at 49 kbar and 299 K. The structure is the same as that of fl-F 2 (Jordan, Streib & Lipscomb, 1964) and )-0 2 (Jordan, Streib, Smith & Lipscomb, 1964;Cox, Samuelsen & Beckurts, 1973).…”

Structure of 'orange' 18O2 at 9.6 GPa and 297 K

“…At 298 K they found that oxygen freezes at 5.9 GPa and then at 9.6 and 9.9 GPa undergoes transitions marked by dramatic color changes. © 1983 International Union of Crystallography STRUCTURE OF 'ORANGE' It is not completely clear how the high-temperature high-pressure phases of oxygen relate to the known low-temperature low-pressure phases which, in order of increasing temperature, are: monoclinic a-O2 (C2/m), rhombohedral fl-O 2 (R3m), and cubic 7-02 (Pm3n) (Donohue, 1974;Cox, Samuelsen & Beckurts, 1973;Mills & Schuch, 1970, unpublished results). At low P and T, 7-0 2 adjoins the melting curve.…”

Low frequency Raman spectra of the liquid and plastic crystal phases of O2, N2, CO, and of Ar crystals with these molecules as guests

“…It ha_s eight molecules per unit cell, six at sites of symmetry 42m and two at sites of m3 symmetry. The character of the orientational disorder is not the same at the two sites, as shown by X-ray (13), neutron diffraction (14), and by Raman studies (1).…”