Abstract
Context. New laboratory investigations of the rotational spectrum of postulated astronomical species are essential to support the assignment and analysis of current astronomical surveys. In particular, considerable interest surrounds sulfur analogs of oxygen-containing interstellar molecules and their isomers. Aims. To enable reliable interstellar searches of vinyl mercaptan, the sulfur-containing analog to the astronomical species vinyl alcohol, we investigated its pure rotational spectrum at millimeter wavelengths. Methods. We extended the pure rotational investigation of the two isomers syn and anti vinyl mercaptan to the millimeter domain using a frequency-multiplication spectrometer. The species were produced by a radiofrequency discharge in 1,2-ethanedithiol. Additional transitions were remeasured in the centimeter band using Fourier-transform microwave spectroscopy to better determine rest frequencies of transitions with low-J and low-Ka values. Experimental investigations were supported by quantum chemical calculations on the energetics of both the [C2,H4,S] and [C2,H4,O] isomeric families. Interstellar searches for both syn and anti vinyl mercaptan as well as vinyl alcohol were performed in the EMoCA spectral line survey carried out toward Sgr B2(N2) with ALMA. Results. Highly accurate experimental frequencies (to better than 100 kHz accuracy) for both syn and anti isomers of vinyl mercaptan are measured up to 250 GHz; these deviate considerably from predictions based on extrapolation of previous microwave measurements. Reliable frequency predictions of the astronomically most interesting millimeter-wave lines for these two species can now be derived from the best-fit spectroscopic constants. From the energetic investigations, the four lowest singlet isomers of the [C2,H4,S] family are calculated to be nearly isoenergetic, which makes this family a fairly unique test bed for assessing possible reaction pathways. Upper limits for the column density of syn and anti vinyl mercaptan are derived toward the extremely molecule-rich star-forming region Sgr B2(N2) enabling comparison with selected complex organic molecules.
Highlights
From the diatomic SH+ and SH radicals (Menten et al 2011; Neufeld et al 2012) to the large complex organic molecule ethyl mercaptan, nearly 20 sulfur-bearing species have been observed in the interstellar medium (ISM) and in the circumstellar envelopes of evolved stars
Besides vinyl mercaptan, other species were produced under our experimental conditions. Some of their transitions were observed with high signal-to-noise ratios, they could not be assigned to any known species using the Cologne Database for Molecular Spectroscopy (CDMS) and NASA Jet Propulsion Laboratory (JPL) catalogs (Endres et al 2016; Pickett et al 1998)
We searched for vinyl mercaptan in the EMoCA spectral line survey performed toward the Sgr B2(N) star-forming region with Atacama Large Millimeter/submillimeter Array (ALMA)
Summary
From the diatomic SH+ and SH radicals (Menten et al 2011; Neufeld et al 2012) to the large complex organic molecule ethyl mercaptan (ethanethiol, C2H5SH; Kolesniková et al 2014), nearly 20 sulfur-bearing species have been observed in the interstellar medium (ISM) and in the circumstellar envelopes of evolved stars. Thioacetaldehyde polymerizes rapidly, with a lifetime on the order of ten seconds (Kroto et al 1974), and it must, as with vinyl mercaptan, be produced in situ for spectroscopic studies To confidently detect these two transient species in the ISM, laboratory measurements at higher frequency are essential, in spectral bands in which ALMA operates. Isomeric family and its isovalent oxygen counterparts via highlevel quantum chemical calculations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
