Top: a) and b) histogram of the linewidths of the CH⁺, ¹³CH⁺, SH⁺ (this work), and HCO⁺ (Godard et al. 2010) velocity components obtained with the multi-Gaussian decomposition procedure (see Table A.1); c) linewidth distributions of CH⁺ and CH observed by Crane et al. (1995) in the local diffuse medium. Bottom: first- (mean) and second- (standard deviation) order moments of the Δυ distributions issued from the combined CH⁺, ¹³CH⁺, and SH⁺ data (red squares) and from the CH⁺ data observed in the solar neighbourhood (blue circles); the moments are computed over increasing Δυ intervals: mean = ; standard deviation = , where N(Δυ) is the linewidth distribution.