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Fig. 4


Abundance relative to H2 as a functionof the H2 column density derived from the submillimeter CH observations at 532 or 536 GHz or from the reddening. The different symbols refer to different sight-lines as noted at top. HCO+ is shown in blue, HF in green, H2O in purple, and CCH in gray. The CCH data were taken with the IRAM-30 m telescope (Gerin et al. 2011) as well as the HCO+ data for W49N and W51 (Godard et al. 2010).

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