Notes. ^(∗) E = absorption line profile observed in the star-forming region; T_ex may be underestimated, hence the lower limit on N(HF), and N(CH). ^(a) From the observations with the VLA interferometer by Koo (1997), Fish et al. (2003), Pandian et al. (2008), Dwarakanath et al. (2004), and Lang et al. (2010) assuming a spin temperature of 100 K. ^(b) From (Gerin et al. 2010b; Gerin et al., in prep.). ^(c) From (Neufeld et al. 2010b; Sonnentrucker et al. 2010; Neufeld et al., in prep.; Sonnentrucker et al., in prep.). ^(d) Estimate from the observation of the CH absorption lines, a mean value of the HF/CH column density ratio of 0.4 (inferred from Cols. 5 and 6) and an abundance ratio n(HF)/n(H₂) = 3.6 × 10^-8, as predicted by UV-dominated chemical models (see Appendix C). ^(e) Estimate from the observation of the HF absorption lines and an abundance ratio n(HF)/n(H₂) = 3.6 × 10^-8, as predicted by UV-dominated chemical models (see Appendix C). ^(f) Estimate of N_H integrated over the entire line of sight from models of the extinction at 2 μm by Marshall et al. (2006). In the last column, the total hydrogen column densities are estimated over the entire sight line.