CH observations of diffuse molecular clouds

A survey of CH 3.3 GHz emission from a sample of high-latitude molecular clouds, diffuse clouds, and heavily reddened globular clusters is presented. The F = 1-1 main-line transition was detected in every molecular cloud in the sample and in two out of four globular cluster lines of sight. The high rate of detections in the low-extinction high-latitude clouds indicates that the CH hyperfine ground-state transitions are at least as efficient low-density molecular gas tracers as the CO rotational transitions. The CH column densities and abundances with respect to H(total) determined for the molecular clouds are consistent with predictions of equilibrium chemistry models for clouds of low extinction and density. Upper limits to the CH abundance for four IRAS cirrus clouds are also consistent with chemistry models for the predominantly atomic hydrogen, warm low-density diffuse clouds which constitute a significant fraction of the interstellar medium. 55 refs