1995A&A...296L...9S

We present an observational study of mm-wave CO⁺ N=2-1, J=5/2-3/2 and J=3/2-1/2 rotational emission from star-forming molecular clouds in Orion, M17 and S140. Intense CO⁺ line emission is produced in the molecular cloud/HII regioninterfaces in the Orion Bar and M17 SW with peak integrated intensities of 1.3 to 1.9Kkm/s in the J=5/2-3/2 line. In S140 we derive an upper limit of 30mK for this line. The observed CO⁺ emission is likely produced in the photon-dominated regions on the surfaces of dense molecular clumps at the cloud edges.