Computational study of the reaction SH + O2.

Area of Science:

• Atmospheric Chemistry
• Chemical Kinetics
• Computational Chemistry

Background:

• Understanding the reaction pathways of sulfur hydride (SH) is crucial for atmospheric chemistry.
• The interaction between SH and molecular oxygen (O2) influences the formation of key atmospheric species.
• Previous studies lacked detailed characterization of the SH + O2 reaction dynamics.

Purpose of the Study:

• To computationally characterize the reaction mechanism and product channels of SH + O2.
• To determine the relative rates and energy barriers for dominant reaction pathways.
• To elucidate the atmospheric implications of SH oxidation.

Main Methods:

• Utilized multireference computational chemistry methods.
• Geometries and vibrational frequencies were calculated using CASSCF/cc-pVTZ.
• Single-point energies were computed at the MRCI/aug-cc-pV(Q+d)Z level.

Main Results:

• Identified SO + OH and HSO + O as the dominant product channels.
• The SO + OH channel has a reaction barrier of ~81 kJ mol-1 and is kinetically favored at room temperature.
• The HSO + O channel is barrierless but endothermic (~89 kJ mol-1), becoming competitive only at high temperatures (>1000 K) due to entropic factors.

Conclusions:

• The atmospheric oxidation of SH predominantly yields SO + OH with a rate coefficient of ~1.0 x 10(-2) cm3 mol-1 s-1.
• Hydrogen abstraction to form S + HO2 is a minor channel due to a high barrier (~165 kJ mol-1).
• Direct sulfur insertion to form SO2 + H is not feasible.