Scatter plot of the difference between the neutral pNH₂D and the ion N₂D⁺ centroid velocity (δV^shift = V^neutral – V^ion) versus the N_H2 column density derived from Herschel and reprojected to the same spatial grid as that of the molecular line data. The scatter in δV^shift is larger for smaller NH₂ values. The color of the data points and the color bar indicate the difference of the ion-neutral total velocity dispersion (δσ_v,tot).