Truman H. Jordan

Single‐Crystal X‐Ray Diffraction Studies of α‐N2 and β‐N2

The structure of α‐N2 is cubic in the space group P213 with four molecules per unit cell. A total of 49 independent observed single‐crystal x‐ray diffraction maxima yield R=Σ ‖Fo|−|Fc ‖ /Σ|Fo|=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 A 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.

Single‐Crystal X‐Ray Diffraction Study of β Nitrogen

Three‐dimensional x‐ray diffraction data have been collected from single crystals of nitrogen at 50°K. The observed general condition, l=2n for hh2hl reflections is in agreement with the previously assigned space group, P63/mmc, and there are two molecules in the unit cell. The data agree equally well with two nearly physically indistinguishable models, in each of which the molecular centers form a hexagonal closest packed (hcp) lattice. In one, the molecule is precessing about the z axis passing through its center, at an angle of 54.5±2.5° between z and the N–N bond, while in the other the nitrogen atoms are statistically distributed among the 24‐fold positions with the molecular axis again at an angle of 54.5° relative to z.

Single‐Crystal X‐Ray Diffraction Study of β‐Fluorine

Three‐dimensional x‐ray diffraction data from a single crystal of β‐F2 have yielded a crystal structure like that later found for the γ‐O2 phase in which no dimers are present. The unit cell is cubic, contains eight molecules, and has a lattice dimension of a=6.67±0.07 A. The two molecules at 000 and ½ ½ ½ are approximately spherically disordered, and the six molecules approximately at ¼ ½ 0, ¾ ½ 0, 0 ¼ ½, 0 ¾ ½, ½ 0 ¼, and ½ 0 ¾ are highly disordered, respectively, in the planes x=¼, x=¾, y=¼, y=¾, z=¼, and z=¾. The value of R=Σ ‖ Fo |−| Fc ‖/Σ | Fo | is 0.10 for the 28 observed reflections.