Enrichment of the nitrogen atomic component with the $^{15}$N isotope in a post-discharge zone

Isotope atomic composition in the post-discharge zone of a pulsed discharge in a nitrogen flow was studied by electron paramagnetic resonance. It is shown that, while the atomic concentration in the post-discharge zone decreases, the relative content of the $^{15}$N isotope increases more than 30 times compared to its natural abundance. Such a high isotope enrichment exceeds more than fourfold the corresponding maximal value that is predicted for the nitrogen atoms by the existing theoretical model. Analysis of the experimental results shows that the isotope-selective dissociation of nitrogen molecules proceeds in the post-discharge zone after the most part of atoms created in the discharge zone had recombined at the tube surface. A mechanism that explains that a nitrogen isotope enrichment as high as that is quite possible is proposed.