2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/129918We present observations of the $J$=1--0, 2--1, and 3--2 rotational transitions of N$_2$H$^+$ and N$_2$D$^+$ towards a sample of prototypical dark clouds. The data have been interpreted using non--local radiative transfer models.12 pages, 18 figuresAstrophysicstext