Top: abundances relative to H nuclei and left-to-right accumulated column densities of the isotopologues of N and N₂ in the modelled interstellar cloud. Bottom: ratios of abundances and column densities of ¹⁴N- and ¹⁵N-bearing species. Also indicated are the adopted elemental ratios of ¹⁴N / ¹⁵N and ¹⁴N₂ / ¹⁴N ¹⁵N (dashed lines).