Irradiation-Produced Paramagnetic Oxides of Nitrogen in Single-Crystal Potassium Azide

A magnetic resonance absorption centered about $g=2\mathrm{}$ and showing no evidence of fine structure is reported in x-irradiated single crystals of potassium azide. Six absorption lines are detected which appear to exhibit axial symmetry about the crystal $C$ direction. These lines are shown to be a composition of two distinct spectra each consisting of three nuclear hyperfine components. For one set of lines, an anisotropic hyperfine splitting varying from 38 to 3 Oe is observed as the magnetic field is rotated from the crystal $C$ axis to a direction perpendicular to this axis. The other set similarly exhibits splittings between 62 and 31 Oe. The inner and outer sets of lines are believed to be due to NO and N${\mathrm{O}}_2$ molecules, respectively, with both molecules located at crystal sites having axial symmetry. These molecular species are formed during the irradiation process, perhaps from nitrate and/or nitrite impurities known to be contained in the lattice. Each of the three components of the outer set of lines exhibits a partially resolved seven-line multiplet structure which is interpreted to be the result of an interaction between the paramagnetic electron and the nuclei of two crystallographically equivalent nearest-neighbor potassium ions.