Dissociative recombination of N${}_2$H${}^{+}$: Isotopic effects

Abstract

The investigation of the isotopic ratio of interstellar nitrogen -- ${}^{14}$N versus ${}^{15}$N -- is done, for explaining its variations observed for N2H+ in different interstellar and Solar environments. The goal is to produce cross sections and rate coefficients for electron impact dissociative recombination for different isotopologues of N${}_2$H${}^{+}$, since it was envisioned as a novel source that can lead to nitrogen fractionation. We calculate dissociative recombination cross sections and rate coefficients using the normal mode approximation combined with the R-matrix theory and vibronic frame transformation within the multichannel quantum defect theory for eight isotopologues containing both ${}^{14}$N, ${}^{15}$N and H, D. Our calculations show that the relative differences respective to the main isotopologue (${}^{14}$N${}_2$H${}^{+}$) is below 1% for the hydrogen containing isotopologues, but reaches almost 30% for the heaviest deuterated isotopologue, leading us to the conclusion that according to the present status of the theory, dissociative recombination is not responsible for the peculiar ${}^{14}$N/${}^{15}$N isotopic ratios of N${}_2$H${}^{+}$ observed in the different interstellar molecular clouds.

7 pages, 8 figures, 2 tables. arXiv admin note: text overlap with arXiv:2305.17976