Mechanism and Kinetics of the Reaction between HS and Cl Radicals

Abstract

The atmospheric reaction between HS and chlorine radicals was studied theoretically, using ab initio methods. We investigated three reaction possibilities: HSCl formation, and the production of HCl and sulfur, singlet and triplet. The channels that lead to HSCl and to HCl and S(3P) are spontaneous and exothermic at 298.15 K, and the channel for HCl and S(1D) formation is nonspontaneous and endothermic. In a microcanonical kinetics calculation, the rate constant we obtained for HSCl formation was 2.4 × 10-11 cm3 molecule-1 s-1 at a pressure of 1 atm, and 2.4 × 10-13 cm3 molecule-1 s-1 at a pressure of 0.01 atm. The rate constant for HCl and triplet sulfur production was not significantly pressure-dependent, and its value was 9.0 × 10-11 cm3 molecule-1 s-1. In the troposphere, the proportion of reaction products predicted was 79% for HCl and S(3P), and 21% for the formation of HSCl. At lower pressures, the proportion of HSCl decreased, and at a pressure of 0.01 atm it was predicted to be practically null. The rate constant for the total reaction was determined to be 1.1 × 10-10 cm3 molecule-1 s-1 at 1 atm. At a pressure of 0.01 atm, this value decreased to 9.0 × 10-11 cm3 molecule-1 s-1, which is within the limit error of the only experimental result known in the literature.

Predicting and characterizing new molecular species at a high-level theoretical approach: HSeCl, HClSe, and SeCl

“…We note that, in the case of HSCl, we have shown that after strong volcanic eruptions, a condition in which the concentration of hydrogen sulfide becomes significant, it is very likely that HSCl can be formed, as well as under high pressures [6,7].…”

“…Although, to the best of our knowledge, no results have been found in the literature on the HSeCl species, neither experimental nor theoretical, our previous investigations on the HSCl/HClS [5][6][7] system motivated us also to explore the selenium analogue on the singlet potential energy surface 1 [H, Se, Cl]. We note that, in the case of HSCl, we have shown that after strong volcanic eruptions, a condition in which the concentration of hydrogen sulfide becomes significant, it is very likely that HSCl can be formed, as well as under high pressures [6,7].…”

Electronic structure and spectra of a new molecular species: SI. A theoretical contribution

“…In regions of strong volcanic eruptions, the possibility that sulfur halides can act also as a halogen reservoir should be examined, and the spectroscopic characterization of SI would offer a means to probe its presence in various gas phase environments. In the case of HSCl [8,9], we have also shown that under these conditions, it is very likely that this species can be formed and play a role in atmospheric chemistry similar to that of its isoelectronic analogue HOCl. Relevant to this context, we also refer the reader to the theoretical work of Roszak et al [13] on the electronic states of IO, to the investigations on emission spectra obtained by high-resolution and laser-induced fluorescent techniques [14][15][16][17], and to the more recent work on the thermochemical properties of halogen oxides by Peterson et al [18].…”

“…In the corresponding sulfur series, very little is known experimentally, and for the two heavier diatomics, SBr and SI, results are practically nonexistent, to the best of our knowledge. Theoretically, the two lighter molecules, SF and SCl, were investigated by Yang and Boggs [4,5], and as part of a long-term project on sulfur halogen species being conducted in our group, not only SCl and SBr [6,7] but potential energy surfaces for closely related triatomic and tetratomic systems like HSCl, HClS [8,9], HSSCl, HSClS, HClS 2 [10], and SSX 2 and XSSX, with X = F and Br [11,12] have been extensively investigated with high level ab initio approaches with focus either on spectroscopy or on structure, stability and thermochemistry. In regions of strong volcanic eruptions, the possibility that sulfur halides can act also as a halogen reservoir should be examined, and the spectroscopic characterization of SI would offer a means to probe its presence in various gas phase environments.…”

Full-dimensional analytical ab initio potential energy surface of the ground state of HOI

“…It is our hope that the tools here developed should prove reliable enough to investigate in a near future the dynamics not only of the [H, O, I] surface, but also of new triatomic systems such as [H, S, X] (X = Cl, Br, and I), described in previous works in our group. [16][17][18] …”