$^{15}$N isotope enrichment of the atomic nitrogen component in atomic-molecular exchange reactions in the post-discharge zone

A kinetic model is presented that explains the more than thirty-fold enrichment of the atomic nitrogen component with the $^{15}$N isotope in the post-discharge zone. Isotopic enrichment is due to the activation nature of the exchange reaction of atoms with vibrationally excited nitrogen molecules, the upper vibrational levels of which are enriched with molecules containing a heavier isotope during non-equilibrium vibrational-vibrational exchange. The dependences of the concentrations of $^{14}$N and $^{15}$N atoms on the time of nitrogen flow through a quartz tube emerging from the region of a pulsed electric discharge are obtained. In addition to exchange, the model took into account the dissociation of molecules, the recombination of atoms, and the loss of the vibrational energy of molecules on the surface of the tube. The obtained dependence of the increase in the ratio of the concentrations of $^{15}$N to $^{14}$N atoms on the time of nitrogen flow through the post-discharge zone satisfactorily describes the experimental data published earlier and obtained in this work.