2005AJ....130.2725M

Spectra in the CH ²Π_1/2, J=1/2, F=1-1 transition at 3335 MHz were obtained in three five-point crosses centered on the Galactic plane at l=50°, 100°, and 110°. The lines of sight traversed both giant molecular clouds (GMCs) and local, smaller entities. This transition is a good tracer of low-density molecular gas, and the line profiles are very similar to CO(1-0) data at nearly the same resolution. In addition, the CH 3335 MHz line can be used to calibrate the CO-H₂conversion factor (X_CO) in low-density molecular gas. Although this technique underestimates X_COin GMCs, our results are within a factor of 2 of X_COvalues calibrated for GMCs by other techniques. The similarity of CH and CO line profiles, and that of X_COvalues derived from CH and more traditional techniques, implies that most of the molecular gas along the observed lines of sight is at relatively low densities (n≤10³/cm3).