Single-crystal x-ray diffraction studies of α-N2 and β-N2

Abstract

The structure of α-N2 is cubic in the space group P2 13 with four molecules per unit cell. A total of 49 independent observed single-crystal x-ray diffraction maxima yield R = ∑ ∥ F 0| -|Fc ∥ /∑| F0| = 0.13. Two faint reflections, (501) and (520), violate the space group Pa3, which yields R = 0.21. Molecular centers are displaced by 0.1 to 0.2 Å from the centrosymmetric positions in Pa3 along the [111] directions so that the symmetry is reduced to P213. Some corrections have been made in the Lorentz factors for upper levels and for the absorption of x rays in the experimental arrangement in the β-N2 study. The value of R improves from 0.09 to 0.04 for the freely rotating model, and the best precession angle is 56.0° rather than 54.5° (both ±2.5°) for the precession model, which we prefer.