Observations of ortho and para thioformaldehyde.

Observations of the 3(12)-2(11) and 3(13)-2(12) transitions of ortho and the 3(03)-2(02) transitions of para H2CS were made with the Onsala and AT&T Bell Laboratories telescopes. The most precise results, for a beamwidth of 1'8 arc, were the para (103 GHz) to ortho (104 GHz) line ratios of 0.51+- 0.04 for Orion and 0.44+-0.05 for DR21 (OH). A higher but less accurate ratio of 0.57+-0.08 was obtained for DR21 (OH) observed with the smaller 0!6 beam. The ortho/para ratios are quite close to the values of ~0.56 derived from a LVG analysis, with the usual densities, kinetic temperatures and collision rates appropriate to H2CO cloud modles, assuming a true para/ortho abundance ratio of 1:3. Observations of the (34)S isotope of H2CS towards Orion gave a line ratio H2C32S/H2C34S of 15 (-3)(+5) for the 3(12)-2(12) transition, not significantly different from the terrestrial [(32)S]/[(34)S] value of 22. Revised estimates of the rest frequencies of the various thioformaldehyde lines observed are given.