Amplification and Absorption of the 9 cm 2Π½ J = ½ A-Doublet Lines of Interstellar CH

Following the detection of the 9 cm ground-state triplet of CH by Rydbeck et al. (1973), preliminary observations at the CH frequencies were made with the Parkes 64-m telescope (beamwidth ∼6‧ arc) in December 1973 and January 1974. We have detected the CH lines in many galactic HII regions and in the direction of the galactic centre.