Thaddeus et al. 1971
Thaddeus, P., R.W. Wilson, M. Kutner, A.A. Penzias, and K.B. Jefferts, 1971: Discovery of para-formaldehyde and the 2-millimeter formaldehyde distribution in the Orion Infrared Nebula. Astrophys. J., 168, L59-L65, doi:10.1086/180785.
The 150.5-GHz line of ortho- and the 145.6-GHz line of para-H2CO have been discovered in Ori A, and a detailed map of the previously detected 140.8-GHz ortho line has been obtainedl H2CO emissions extends over a region whose dimensions are ~ 3'×5', whose neutral-particle density is calculated to be ~ 2×105 /cm3, and whose total mass is ~ 200 M—; it is argued that the Kleinmann-Low infrared nebula is the central condensation of this cloud. The 140.8-GHz line has also now been found in Sgr A, W3(OH), and W51.