A search for 2Pi, N=1, J=3/2 Lambda-doubling transitions of CH.

The authors report negative results for a search for the ²Π, N = 1, J = 3/2 Λ-doubling transition of the CH molecule. Upper limits to the column densities calculated from these observations are in agreement with those previously derived from the 3 GHz ground-state transitions, provided that the excitation temperature within the Λ-doublet is ⪉100 - 700K. Toward Cas A, Ori A, and Sgr B2, upper limits to the optical depth for the transition are an order of magnitude lower than those obtained from the ground-state measurements.