Left: Map of the difference between the neutral (pNH₂D) and the ion (N₂D⁺) total velocity dispersion ($\delta {\sigma }_{\mathrm{v},\mathrm{t}\mathrm{o}\mathrm{t}}={\sigma }_{\mathrm{v},\mathrm{t}\mathrm{o}\mathrm{t}}^{\mathrm{n}\mathrm{e}\mathrm{u}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{l}}-{\sigma }_{\mathrm{v},\mathrm{t}\mathrm{o}\mathrm{t}}^{\mathrm{i}\mathrm{o}\mathrm{n}}$). Right: Histogram of δσ_v,tot in black and of δσ_v,NT in gray. The vertical dashed black and gray lines indicate the mean values for the δσ_v,tot and δσ_v,NT distributions, respectively. The mean and standard deviation for δσ_v,tot are –0.004 km/s and 0.006 km/s, and for δσ_v,NT are –0.007 km/s and 0.014 km/s, respectively.