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The recombination of S atoms has been found to be stepwise from the smallest unit, the elemental S atom, to the most abundant molecule S8. The reaction between S + S2 → S3 has not been reported either experimentally or by theory, but may be a key intermediate step in the formation of sulfur aerosols in low-O2 atmospheres. In this work, the kinetics of this reaction is reported with Ar gas used as the chaperone molecule in the production of S3 via two complex intermediates: SAr + S2 and S2Ar + S. Quasi-classical and classical trajectory methods are used. The rate constant of the S + S2 + Ar → S3 + Ar reaction is determined to be 2.66 × 10-33 cm6 mol-1 s-1 at 298.15 K. The temperature dependence of the reaction is found to be 2.67 × 10-33 exp[143.56(1/T-1/298.15)]. The second-order rate constant of S + S2 → S3 is 6.47 × 10-14 cm3 molecule-1 s-1 at 298.15 K and the Arrhenius-type rate constant is calculated to be 6.25 × 10-14 exp[450.15(1/T-1/298.15)] cm3 molecule-1 s-1. This work provides a rate coefficient for a key intermediate species in studies of sulfur formation in the modern Venus atmosphere and the primitive Earth atmosphere, for which assumed model rate coefficients have spanned nearly 4 orders of magnitude. Although a symmetry-induced mass-independent isotope effect is not expected for a chaperone mechanism, the present work is an important step toward evaluating whether mass-independence is expected for thiozone formation as is observed for ozone formation. [ABSTRACT FROM AUTHOR]

Accurate calculations of the low-lying singlet and triplet electronic states of thiozone, S3, have been carried out using large multireference configuration interaction wave functions. Cuts of the full potential energy surfaces along the stretching and bending coordinates have been presented, together with the vertical excitation spectra. The strong experimentally observed absorption around 395 nm is assigned to the 1 1B2 state, which correlates to ground state products. Absorption at wavelengths shorter than 260 nm is predicted to lead to singlet excited state products, S2 (a 1Δg)+S(1D). The spectroscopic properties of the X 3Σg-, a 1Δg, and b 1Σg+ electronic states of the S2 radical have also been accurately characterized in this work. The investigations of the low-lying electronic states were accompanied by accurate ground state coupled cluster calculations of the thermochemistry of both S2 and S3 using large correlation consistent basis sets with corrections for core-valence correlation, scalar relativity, and atomic spin-orbit effects. Resulting values for D0(S2+S) and ∑D0 for S3 are predicted to be 61.3 and 162.7 kcal/mol, respectively, with conservative uncertainties of ±1 kcal/mol. Analogous calculations predict the C2v-D3h (open-cyclic) isomerization energy of S3 to be 4.4±0.5 kcal/mol. [ABSTRACT FROM AUTHOR]

Accurate calculations of the low-lying singlet and triplet electronic states of thiozone, S3, have been carried out using large multireference configuration interaction wave functions. Cuts of the full potential energy surfaces along the stretching and bending coordinates have been presented, together with the vertical excitation spectra. The strong experimentally observed absorption around 395 nm is assigned to the 1 1B2 state, which correlates to ground state products. Absorption at wavelengths shorter than 260 nm is predicted to lead to singlet excited state products, S2 (a 1Δg)+S(1D). The spectroscopic properties of the X 3Σg-, a 1Δg, and b 1Σg+ electronic states of the S2 radical have also been accurately characterized in this work. The investigations of the low-lying electronic states were accompanied by accurate ground state coupled cluster calculations of the thermochemistry of both S2 and S3 using large correlation consistent basis sets with corrections for core-valence correlation, scalar relativity, and atomic spin-orbit effects. Resulting values for D0(S2+S) and ∑D0 for S3 are predicted to be 61.3 and 162.7 kcal/mol, respectively, with conservative uncertainties of ±1 kcal/mol. Analogous calculations predict the C2v-D3h (open-cyclic) isomerization energy of S3 to be 4.4±0.5 kcal/mol. [ABSTRACT FROM AUTHOR]

Observation of mass-dependent and non-mass-dependent sulfur isotope fractionations in elemental sulfur is providing new insight into the nature of the sulfur cycle in the atmosphere. Interpretation of the experimental isotope data requires estimation of the energetics for the reaction S+S2→S3 (isoelectronic with O+O2→O3). Key molecular properties of the S3 potential-energy surface, such as vibrational frequencies and isotopic shifts, are presented that can be used to assess the mass-dependent fractionation effect. Ab initio results are compared to the available experimental results for S2 to evaluate the reliability of the computational results for S3. The S–S bond dissociation energy for S3 is determined to be 60.9±1 kcal mol-1. [ABSTRACT FROM AUTHOR]

Observation of mass-dependent and non-mass-dependent sulfur isotope fractionations in elemental sulfur is providing new insight into the nature of the sulfur cycle in the atmosphere. Interpretation of the experimental isotope data requires estimation of the energetics for the reaction S+S2→S3 (isoelectronic with O+O2→O3). Key molecular properties of the S3 potential-energy surface, such as vibrational frequencies and isotopic shifts, are presented that can be used to assess the mass-dependent fractionation effect. Ab initio results are compared to the available experimental results for S2 to evaluate the reliability of the computational results for S3. The S–S bond dissociation energy for S3 is determined to be 60.9±1 kcal mol-1. [ABSTRACT FROM AUTHOR]

Accurate calculations of the low-lying singlet and triplet electronic states of thiozone, S(3), have been carried out using large multireference configuration interaction wave functions. Cuts of the full potential energy surfaces along the stretching and bending coordinates have been presented, together with the vertical excitation spectra. The strong experimentally observed absorption around 395 nm is assigned to the 1 (1)B(2) state, which correlates to ground state products. Absorption at wavelengths shorter than 260 nm is predicted to lead to singlet excited state products, S(2) (a (1)Delta(g))+S((1)D). The spectroscopic properties of the X (3)Sigma(g) (-), a (1)Delta(g), and b (1)Sigma(g) (+) electronic states of the S(2) radical have also been accurately characterized in this work. The investigations of the low-lying electronic states were accompanied by accurate ground state coupled cluster calculations of the thermochemistry of both S(2) and S(3) using large correlation consistent basis sets with corrections for core-valence correlation, scalar relativity, and atomic spin-orbit effects. Resulting values for D(0)(S(2)+S) and SigmaD(0) for S(3) are predicted to be 61.3 and 162.7 kcal/mol, respectively, with conservative uncertainties of +/-1 kcal/mol. Analogous calculations predict the C(2v)-D(3h) (open-cyclic) isomerization energy of S(3) to be 4.4+/-0.5 kcal/mol.

Observation of mass-dependent and non-mass-dependent sulfur isotope fractionations in elemental sulfur is providing new insight into the nature of the sulfur cycle in the atmosphere. Interpretation of the experimental isotope data requires estimation of the energetics for the reaction S+S2-->S3 (isoelectronic with O+O2-->O3). Key molecular properties of the S3 potential-energy surface, such as vibrational frequencies and isotopic shifts, are presented that can be used to assess the mass-dependent fractionation effect. Ab initio results are compared to the available experimental results for S2 to evaluate the reliability of the computational results for S3. The S-S bond dissociation energy for S3 is determined to be 60.9+/-1 kcal mol(-1).