References. (1) Jansen et al. (1995); (2) Schilke et al. (2001); (3) van Dishoeck et al. (1993); (4) Marcelino et al. (2009); (5) Tercero et al. (2010); (6) Tercero et al. (in prep.); (7) Marcelino (2007); (8) Martín et al. (2006); (9) Wang et al. (2004); (10) Martín et al. (2009a); (11) Bayet et al. (2009); (12) Downes et al. (1992); (13) Meier & Turner (2005); (14) Usero et al. (2006).

Notes. Galactic sources: The second value of the H¹³CO⁺, HN¹³C, and H¹³CN abundances has been derived from the main isotope assuming a ¹²C/¹³C isotopic ratio of 65 for the Orion Bar and the SNR IC 443−G. Extragalactic sources: a source size of 20′′ (Martín et al. 2006; Wang et al. 2004) has been assumed in our column density estimations of M 82 and IC 342 from single-dish observations, as well as optically thin emission and the LTE approximation. For that purpose, integrated intensities have been taken from the compilation made by Martín et al. (2006) plus additional data taken from Martín et al. (2009a) and Bayet et al. (2009). The second values of the H¹³CO⁺, HN¹³C, and H¹³CN abundances have been derived from the main isotopes assuming ¹²C/¹³C  ≃  40 (Henkel et al. 1998). Interferometric IC 342 abundances have been derived from the parameters of the line profiles taken from Usero et al. (2006), Meier & Turner (2005), and Downes et al. (1992), assuming a source size of 6′′, optically thin emission, and the LTE approximation. CS abundance has been derived from C³⁴S assuming ³²S/³⁴S  ~  8−23 (Meier & Turner 2005).