Formaldehyde observations of giant molecular clouds

The excitation of H/sub 2/CO noted in the absorption toward a number of Galactic continuum radio sources has been investigated on the basis of the 2 cm and 6 cm K-doublet transitions. The data are analyzed using a 16-level collisional excitation model and the collisional rate coefficients of Green et al. (1978). Median H/sub 2/ densities of 90,000/cu cm for clouds near the H I regions, and 70,000/cu cm for clouds distant from the H II regions, are found. Estimates of the total ortho-H/sub 2/CO column density have been obtained, indicating that the H/sub 2/CO traces a significant fraction of the total column density seen in CO. 41 references.