28-30 September 2016
Tagungstätte Schloss Ringberg, Kreuth
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Tagungstätte Schloss Ringberg, Kreuth -

Sulfur-bearing molecular species: Rotational spectroscopy and quantum-chemical computations at the LMSB



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Detection of ``new'' species. There is a great interest in understanding which molecular species containing sulfur might be observed in the ISM. The work along this line concerns the investigation of radicals and ionic species, guided by high accuracy state-of-the-art quantum-chemical computations. Among radicals, we mention HSO. High-resolution measurements of its rotational spectrum have been carried out within a frequency range well up into the THz region. Subsequently, a rigorous search for HSO in the two most studied high-mass star-forming regions, Orion KL and Sagittarius (Sgr) B2, and in the cold dark cloud Barnard 1 (B1-b) has been performed [1]. The corresponding cation, HSO$^+$, and the cationic radical species HCCS$^+$ are still under investigation. For both of them, experimental information are missing and laboratory measurements are entirely guided by quantum-chemical computations.

Zeeman effect. The Zeeman effect is the only available technique for directly measuring magnetic field strengths in interstellar clouds. Unfortunately, most of the common interstellar molecules are closed-shell species (non-paramagnetic species) and therefore they do not show any Zeeman effect. To our knowledge, the Zeeman effect has been detected unambiguously in non-masing interstellar gas only in HI, OH, and CN lines. Since SO is a promising candidate, the Zeeman effect has been investigated in laboratory for several rotational transitions. For those showing the strongest effect, field intensities in the 6-130 Gauss range have been used to measure the corresponding Zeeman components and to derive accurate values of the $g$ factors [2].

Hyperfine structure. Another important aspect of rotational spectroscopy applied to molecular astrophysics is the observation, if the case, of the hyperfine structure of the rotational spectra. In fact, this would allow gaining information on column densities and kinematics. In particular, the omission of taking the hyperfine structure into account can lead to an overestimation of the line width of the molecular emission lines, and thus to unrealistic abundances of the species under consideration. In this respect, hyperfine structures in the rotational spectra of hydrogen sulfide (H$_2$S) [3] and its mono-deuterated isotopologue HDS [4] have been investigated, with the corresponding analysis guided by accurate quantum-chemical computations.


[1] Cazzoli, G.; Lattanzi, V., Kirsch, T.; Gauss, J.; Tercero, B.; Cernicharo, J.; Puzzarini, C., A&A (2016) in press. DOI:10.1051/0004-6361/201628745

[2] Cazzoli, G.; Lattanzi, V., Coriani, S.; Gauss, J.; Puzzarini, C., in preparation (2016).

[3] Cazzoli, G.; Puzzarini, C., J. Mol. Spectrosc. 298 (2014) 31-37.

[4] Cazzoli, G.; Gauss, J.; Puzzarini, C., in preparation (2016).


The interest on sulfur-bearing molecular species lies on the fact that, despite molecules already detected in the interstellar medium, the sulfur chemistry in space is largely unknown. The chemical form of the missing sulfur has yet to be identified. In the frame of what we can denote as ``sulfur-chemistry issue'', at the Laboratory of Millimeter-/submillimeter-wave Spectroscopy of Bologna (LMSB) radicals, ions and neutral species containing sulfur have been investigated in the last years in view of predicting new species to be observed in space as well as to better characterize those already detected.