Spectroscopic characterization and photochemistry of the vinylsulfinyl radical

A-Band Absorption Spectrum of the ClSO Radical: Electronic Structure of the Sulfinyl Group

Sulfur oxide species (RSOx) play a critical role in many fields, ranging from biology to atmospheric chemistry. Chlorine-containing sulfur oxides may play a key role in sulfate aerosol formation in Venus' cloud layer by catalyzing the oxidation of SO to SO2 via sulfinyl radicals (RSO). We present results from the gas-phase UV-vis transient absorption spectroscopy study of the simplest sulfinyl radical, ClSO, generated from the pulsed-laser photolysis of thionyl chloride at 248 nm (at 40 Torr of N2 and 292 K). A weak absorption spectrum from 350 to 480 nm with a peak at 385 nm was observed, with partially resolved vibronic bands (spacing = 226 cm-1), and a peak cross section σ(385 nm) = (7.6 ± 1.9) × 10-20 cm2. From ab initio calculations at the EOMEE-CCSD/ano-pVQZ level, we assigned this band to 12A' ← X2A″ and 22A' ← X2A″ transitions. The spectrum was modeled as a sum of a bound-to-free transition to the 12A' state and a bound-to-bound transition to the 22A' state with similar oscillator strengths; the prediction agreed well with the observed spectrum. We attributed the vibronic structure to a progression in the bending vibration of the 22A' state. Further calculations at the XDW-CASPT2 level predicted a conical intersection between the excited 12A' and 22A' potential energy surfaces near the Franck-Condon region. The geometry of the minimum-energy conical intersection was similar to that of the ground-state geometry. The lack of structure at shorter wavelengths could be evidence of a short excited-state lifetime arising from strong vibronic coupling. From simplified molecular orbital analysis, we attributed the ClSO spectrum to transitions involving the out-of-plane π/π* orbitals along the S-O bond and the in-plane orbital possessing a σ/σ* character along the S-Cl bond. We hypothesize that these orbitals are common to other sulfinyl radicals, RSO, which would share a combination of a strong and a weak transition in the UV (near 300 nm) and visible (400-600 nm) regions.

Correcting the Experimental Enthalpies of Formation of Some Members of the Biologically Significant Sulfenic Acids Family

Sulfenic acids are important intermediates in the oxidation of cysteine thiol groups in proteins by reactive oxygen species. The mechanism is influenced heavily by the presence of polar groups, other thiol groups, and solvent, all of which determines the need to compute precisely the energies involved in the process. Surprisingly, very scarce experimental information exists about a very basic property of sulfenic acids, the enthalpies of formation. In this Article, we use high level quantum chemical methods to derive the enthalpy of formation at 298.15 K of methane-, ethene-, ethyne-, and benzenesulfenic acids, the only ones for which some experimental information exists. The methods employed were tested against well-known experimental data of related species and extensive CCSD(T) calculations. Our best results consistently point out to a much lower enthalpy of formation of methanesulfenic acid, CH₃SOH (Δ_fH⁰(298.15K) = -35.1 ± 0.4 kcal mol^-1), than the one reported in the NIST thermochemical data tables. The enthalpies of formation derived for ethynesulfenic acid, HC≡CSOH, +32.9 ± 1.0 kcal/mol, and benzenesulfenic acid, C₆H₅SOH, -2.6 ± 0.6 kcal mol^-1, also differ markedly from the experimental values, while the enthalpy of formation of ethenesulfenic acid CH₂CHSOH, not available experimentally, was calculated as -11.2 ± 0.7 kcal mol^-1.

Generation and reactivity of vinyltelluryl radical

Vinyltelluryl radical was prepared by high-vacuum flash pyrolysis from the corresponding divinylditelluride and trapped in an argon matrix at 10 K. The title compound was characterized by IR and UV/Vis spectroscopy, and all experimental data match well with density functional theory at the UB3LYP/def2-QZVPP level. According to UB3LYP/def2-QZVPP computations, the spin density is mainly localized on the Te atom. The vinylogy principle for the vinyltelluryl radical is not applicable due to the lack of delocalization of spin density. Upon irradiation of the matrix with light (λ = 365 nm), the vinyltelluryl radical rearranges to a H-Te˙⋯acetylene complex. Doping the matrix with molecular oxygen leads to the hitherto unknown vinyltelluro peroxy radical. The latter isomerizes to the more thermodynamically stable vinyltelluroyl radical by irradiation with light at λ = 523 nm.