CN in dark interstellar clouds

Observations have been made at 113 GHz of the N = 1-0 transition of CN toward seven positions in six dark clouds. Five clouds were detected. Millimeter CN lines were detected for the first time toward dark clouds outside Taurus. The weakest hyperfine component of N = 1-0 (which has only about 1 percent of the total intensity of N = 1-0 for optically thin LTE conditions) was detected for the first time. The six detected positions were also observed at 226 GHz for N = 2-1 transitions of CN; detections were made at two positions. Evidence for self-absorption was found toward a position in the Rho Oph dark cloud and possibly toward the TMC-1 cloud. Possible non-LTE hyperfine excitation was also observed. The weakness of CN lines is explained by the low level of excitation rather than by low column densities. Comparison with time-dependent astrochemical theory shows that most of our results are compatible with the low-metallicity, steady state (age greater than 100 million yr) abundance calculations.