HyGAL II: The absorption line survey with the IRAM 30m telescope

We present the absorption line survey carried out with the 30 m telescope toward 15-millimeter continuum sources to investigate the molecular content of the diffuse interstellar medium in the Galactic plane. In combination with absorption line observations of six hydrides (ArH+, H2O+, OH+, SH, OH, CH), C+ and O taken with the SOFIA telescope for the SOFIA Legacy Program ``HyGAL'', this survey searching for simple molecular species (e.g., CS, SO, C2H, c-C3H2, HCN, HNC, HCO+, HOC+, and H2S) will provide key constraints on astrochemical models for the diffuse interstellar medium.