Reaction mechanism, energetics, and kinetics of the water-assisted thioformaldehyde + ˙OH reaction and the fate of its product radical under tropospheric conditions

The reaction of thioformaldehyde with OH radical assisted by a single water molecule in the atmosphere is negligible.

Thermal Decomposition Mechanism for Ethanethiol

The thermal decomposition of ethanethiol was studied using a 1 mm × 2 cm pulsed silicon carbide microtubular reactor, CH₃CH₂SH + Δ → Products. Unlike previous studies these experiments were able to identify the initial ethanethiol decomposition products. Ethanethiol was entrained in either an Ar or a He carrier gas, passed through a heated (300-1700 K) SiC microtubular reactor (roughly ≤100 μs residence time) and exited into a vacuum chamber. Within one reactor diameter the gas cools to less than 50 K rotationally, and all reactions cease. The resultant molecular beam was probed by photoionization mass spectroscopy and IR spectroscopy. Ethanethiol was found to undergo unimolecular decomposition by three pathways: CH₃CH₂SH → (1) CH₃CH₂ + SH, (2) CH₃ + H₂C═S, and (3) H₂C═CH₂ + H₂S. The experimental findings are in good agreement with electronic structure calculations.

Do the mercaptocarbene (H–C–S–H) and selenocarbene (H–C–Se–H) congeners of hydroxycarbene (H–C–O–H) undergo 1,2-H-tunneling?

The principal purpose of this investigation is the determination of the tunneling half-lives of the trans-HCSH → H2CS and the trans-HCSeH → H2CSe unimolecular isomerization reactions at temperatures close to 0 K. To aid these determinations, accurate electronic structure computations were performed, with electron correlation treatments as extensive as CCSDT(Q) and basis sets as large as aug-cc-pCV5Z, for the isomers of [H,H,C,S] and [H,H,C,Se] on their lowest singlet surfaces and for the appropriate transition states yielding structural data for key stationary points characterizing the isomerization reactions. The computational results were subjected to a focal-point analysis (FPA) that yields accurate relative energies with uncertainty estimates. The tunneling half-lives were determined by a simple Eckart-barrier approach and via the more sophisticated though still one-dimensional Wentzel–Kramers–Brillouin (WKB) approximation. Only stationary-point information is needed for the former while an intrinsic reaction path (IRP) is necessary for the latter approach. Both protocols suggest that, unlike for the parent hydroxymethylene (HCOH), at the low temperatures of matrix isolation experiments no tunneling will be observable for the trans-HCSH and trans-HCSeH systems.

Infrared spectrum of carbon trisulfide in solid argon

Cocondensation of carbon disulfide with high-frequency discharged argon at 4 K produced carbon monosulfide and atomic sulfur, which reacted spontaneously upon annealing to form the carbon trisulfide molecule as identified from the multiplets observed in mixed (12)C, (13)C and (32)S, (34)S isotopic spectra. On the basis of isotopic substitution and theoretical frequency calculations, infrared absorptions at 1263.3 and 570.1 cm(-1) were assigned to predominantly CS stretching and bending vibrations of CS(3) in solid argon. The CS(3) molecule, which was calculated to have a singlet ground state with C(2v) symmetry, dissociated to form the weakly bound SCS-S complex upon visible light irradiation.