On the Detectability of the HSS, HSO, and HOS Radicals in the Interstellar Medium

Abstract

HSS has yet to be observed in the gas phase in the interstellar medium (ISM). HSS has been observed in cometary material and in high abundance. However, its agglomeration to such bodies or dispersal from them has not been observed. Similarly, HSO and HOS have not been observed in the ISM, either, even though models support their formation from reactions of known sulfur monoxide and hydrogen molecules, among other pathways. Consequently, this work provides high-level, quantum chemical rovibrational spectroscopic constants and vibrational frequencies in order to assist in interstellar searches for these radical molecules. Furthermore, the HSO −HOS isomerization energy is determined to be 3.63 kcal mol −1 , in line with previous work, and the dipole moment of HOS is 36% larger at 3.87 D than HSO, making the less stable isomer more rotationally intense. Finally, the S−S bond strength in HSS is shown to be relatively weak at 30% of the typical disulfide bond energy. Consequently, HSS may degrade into SH and sulfur atoms, making any ISM abundance of HSS likely fairly low, as recent interstellar surveys have observed.

First Detection of Interstellar S2H

“…The channel towards HSO + + H 2 reaction is endothermic in opposite to the channels towards S 2 H + + H 2 and S2H2++H. Therefore, in gas phase the formation of S 2 H is favored relative to HSO. HSO and related species have not been observed in space thus far (Cazzoli et al 2016; Fortenberry & Francisco 2017). Laboratory experiments demonstrate that grain surface chemistry involving H 2 O and H 2 S also present different pathways.…”

“…Martín-Doménech et al (2016a) unsuccesfully searched for S 2 H and H 2 S 2 in the gas phase toward the well-known hot corino, IRAS 16293−2422. The lack of gaseous S 2 H and H 2 S 2 was interpreted as the consequence of the rapid destruction of these species once sublimated in such a warm and dense environment (Martín-Doménech et al 2016a; Fortenberry & Francisco 2017).…”

The Trifluoromethyl Sulfinyl and Oxathiyl Radicals

“…was intensively investigated with quantum chemical computations . According to the latest theoretical study, HSO . is slightly lower in energy than HOS .…”

Spectroscopic Identification of H2NSO and syn‐ and anti‐HNSOH Radicals

“…Weak interactions between these two fragments in the same solid matrix cages can be evidenced by the changes of the IR frequencies of H 2 O( e ',F igure 2B,3 709.5, 3597.2, and 1616.1 cm À1 , N 2 -matrix) and SN (j, Figure 2B,1 208.7 cm À1 )i n comparison to those observed of free H 2 O( 3727.3, 3634.8, and 1597.3 cm À1 ,N 2 -matrix) and SN (1209.4 cm À1 ,Ar-matrix). [23] Similar to HSO, [24] CH 3 SO, [9] and CF 3 SO, [10] H 2 NSO is significantly lower in energy than the isomeric oxathiyl radical H 2 NOS by 46.0 kcal mol À1 . ForH 2 NSO,two conformers differing by 1.6 kcal mol À1 in energy (CCSD(T)/augcc-pVTZ//B3LYP/6-311 ++G(3df,3pd) were located as true minima, and the more stable C ssymmetric conformer displays syn-configuration between the bisector of the HNH angle and the S = Obond.…”