Notes. ^(∗) E = absorption line profile observed in the star-forming region; T_ex may be underestimated, hence the lower limit on N(CH⁺), N(¹³CH⁺), and N(SH⁺). 1,2,3,4,5 = velocity intervals where ¹²CH⁺ and ¹³CH⁺ are observed simultaneously with a 3σ detection level. ^(a) Galactocentric distances derived as with R₀ = 8.5 kpc and θ₀ = 220 km s^-1 as recommended by the IAU (Kerr & Lynden-Bell 1986), and assuming a flat Galactic rotation curve (θ(R_G) = θ₀). ^(b) Towards SgrA*+50 and SgrB2(N), when the comparison is possible, N(CH⁺) derived from ¹²CH⁺ and ¹³CH⁺ and the ratios r₁₂ and r₁₃ agree within the combination of their respective errors and the uncertainty of 50% on the ¹²C/¹³C ratio (see main text). The two last columns contain the ratios r₁₂ = N(SH⁺)/N(CH⁺) and r₁₃ = N(SH⁺)/N(¹³CH⁺) × ¹³C/¹²C. In Col. 10, CH⁺ column densities are inferred from those of ¹³CH⁺ and the ¹²C/¹³C Galactic gradient derived by Milam et al. (2005): N(CH⁺) = N(¹³CH⁺) × ¹²C/¹³C. The blank spaces correspond to unusable ¹³CH⁺ or SH⁺ data owing to the contamination of an emission line from the SFRs, or because the spectrum measured over the associated velocity interval could not be deconvolved from the SH⁺ hyperfine structure.