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Nitrogen has two solid phases, a and 13, being stable below and above phase transition point, T = 35. 61K, respectively. However, a number of other solid phases have been observed at high pressures.
The structure of the low phase of solid nitrogen was investigated by neutron powder diffraction technique. Nitrogen of high purity with natural isotopic abundance was used. A method was used to form high quality powder specimens with randomly oriented fine grains directly form the gas phase. A special sample tube set - up was used which did not produce any extra peaks in the neutron powder diffraction patterns.
The neutron powder diffraction patterns were recorded with two wavelengths (1. 3702 A and 2. 1223 A) using two different diffractometers each of them having five counters. The diffraction patterns recorded with different counters were treated separately but the results obtained from them are consistent with each other. No departure from the cubic structure Was observed even with the long wavelegth The edgelength of the primitive unit cell at 4. 2 K was found to be a==S. 650+ 0. 001 A, slightly higher than was reported earlier.