2023MNRAS.526.3673P

We use spectra and maps of the J = 1 - 0 and J = 2 - 1 DCO⁺, DCN, DNC, $\rm N_2D^+$ lines, and 1₁₁-1₀₁ ortho- and para-NH₂D lines, obtained with the Institut de Radioastronomie Millimétrique (IRAM)-30 m telescope, as well as observations of their hydrogenated isotopologues to study deuteration processes in five high-mass star-forming regions. The temperature was estimated from CH ₃CCH lines, also observed with the IRAM-30 m telescope, and from NH ₃ lines, observed with the 100 m radio telescope in Effelsberg, as well as using the integrated intensity ratios of the J = 1 - 0 H¹³CN and HN¹³C lines and their main isotopologues. Applying a non-local thermodynamic equilibrium radiative transfer model with RADEX, the gas density and the molecular column densities were estimated. D/H ratios are 0.001-0.05 for DCO⁺, 0.001-0.02 for DCN, 0.001-0.05 for DNC, and 0.02-0.4 for NH₂D. The D/H ratios decrease with increasing temperature in the range of 20-40 K and slightly vary at densities $n(\rm H_2) \sim 10^4\!-\!10^6$ cm^–3. The deuterium fraction of $\rm N_2H^{+}$ is 0.008-0.1 at temperatures in the range of 20-25 K and at a density of ∼10⁵ cm^–3. We also estimate relative abundances and find ∼10^–11-10^–9 for DCO⁺ and DNC, ∼10^–11-10^–10 for $\rm N_2D^+$, and ∼10^–10-10^–8 for NH₂D. The relative abundances of these species decrease with increasing temperature. However, the DCN/H₂ ratio is almost constant (∼10^–10). The observational results agree with the predictions of chemical models (although in some cases there are significant differences).