Microwave Detection of Thioformaldehyde

Abstract

Thioformaldehyde (H(2)CS) has been detected and characterized from its microwave spectrum. Preliminary analysis of rotational transitions for the sulfur-32-containing form of H(2)CS shows this new species to have C(2v) symmetry with rotational constants (in megahertz) of A = 292,729, B = 17,698, and C = 16,652. The possibility of detection of thioformaldehyde in the interstellar medium is discussed, and a table of transitions expected to be of importance for that detection is presented.

High‐Frequency Rotational Spectrum of Thioformaldehyde, H2CS, in the Ground Vibrational State

“…Thioformaldehyde is also found toward the Galactic center, in well-known hot cores such as the Compact Ridge in Orion KL, and in outflows such as those of the Cepheus A star-forming region, where it is a tracer of high-velocity gas (Codella et al 2005) and is either desorbing from grains or rapidly forming in the gas-phase after mantle evaporation. Although an interstellar search for thioformaldehyde was carried out ( Evans et al 1970) soon after the first microwave laboratory study (Johnson & Powell 1970), the first interstellar detection was reported a few years later (Sinclair et al 1973). Meanwhile, the extension of the known rotational spectrum to higher microwave and millimeter-wave frequencies (Johnson et al 1971;Beers et al 1972) allowed predictions of a large number of unmeasured lines to be made available for interstellar identification of thioformaldehyde .…”

“…Since the first microwave study of the rotational spectrum of its main isotopic species (Johnson & Powell 1970), a variety of subsequent spectroscopic investigations of thioformaldehyde and its assorted isotopologues have been carried out. The original microwave detection, through 35 GHz, was followed by microwave measurements through 70 GHz, in which mainly Q-branch (ÁJ ¼ 0) transitions were assigned up to J 00 ¼ 27 and K 00 a ¼ 2 (Johnson et al 1971).…”

Do the mercaptocarbene (H–C–S–H) and selenocarbene (H–C–Se–H) congeners of hydroxycarbene (H–C–O–H) undergo 1,2-H-tunneling?

“…The spectrum of thioformaldehyde has been the subject of several experimental studies in the microwave (MW) [12][13][14][15] , millimeter-wave 16 , and infrared ranges 15,[17][18][19][20] . The structure of H 2 CS is very similar to that of formaldehyde (with a significantly shorter r(C-H) and an r(C=S) estimate of 1.611 Å 21 ); it is an a-type asymmetric top molecule with a sizable dipole moment of 1.6491(4) D 22 .…”

Importance of collisional rates for anomalous absorption in H2CC molecule

“…The first microwave spectrum of thioformaldehyde (H 2 CS) was investigated by Johnson and Powell (1970). Following this study, interstellar search for 1 10 -1 11 transition of H 2 CS was carried out by Evans et al (1970) and Davies et al (1971), which remained unsuccessful.…”