H2CO emission at 2 millimeters in dark clouds

The paper reports the detection of the 2-mm emission line due to the 2(12)-1(11) transition of H2CO at two positions in the Taurus dark cloud and one position in the dark cloud L134 N. The profiles of the observed emissions are plotted, and peak radiation temperatures at 2 mm are determined for the three positions. These radiation temperatures are used along with data on the 2-mm H2CO absorption line and computed cross sections for H2-H2CO collisions to deduce the molecular hydrogen density and the ortho-H2CO column density in the two clouds. The results are shown to support previous theoretical estimates of the H2CO/H2 and the H2(C-12)O/H2(C-13)O ratios. It is concluded that if the abundances of CS and HCN in the clouds are equal to that of H2CO, emissions from these molecules should be easily detectable.