Observations of ortho- and para-thioformaldehyde

Abstract

In the present observational study of the 3(12) - 2(11) and 3(13) - 2(12) transitions of ortho-H2CS and the 3(03) - 2(02) transitions of para-H2CS, the most precise results, for a beamwidth of 1.8 arcmin, were the para- and ortho- line ratios of 0.51 + or - 0.04 for Orion and 0.44 + or - 0.05 for DR 21 (OH). The ortho/para ratios are close to the values of about 0.56 derived from a large velocity gradient analysis employing the densities, kinetic temperatures and collision rates appropriate to H2CO cloud molecules, assuming a true para/ortho abundance ratio of 1:3. Revised estimates of the rest frequencies of the various formaldehyde lines observed are given.