Quantum chemical and RRKM calculations of reactions in the H/S/O system

Quantum chemical calculations at the MRCI/aug-cc-pV5Z level are used to describe the conversions between HSO, HOS, H + SO, S + OH and O + SH on the doublet H/S/O potential energy surface. An RRKM analysis of this multiple-well system was carried out in the temperature range 300-2000 K between 0.1 and 10 atm. At these pressures, the stabilization reaction H + SO → HSO or HOS is at the low pressure limit, and stabilization from S + OH and O + SH was not detected. The reactions S + OH → H + SO and O + SH → H + SO were found to be barrierless and very fast at room temperature (4 × 10¹⁴ and 1.5 × 10¹⁴ cm³ mol⁻¹ s⁻¹, respectively). The reaction channel O + SH → S + OH is two orders of magnitude slower than the more exothermic O + SH → H + SO reaction, although a second pathway involving direct H-abstraction (O + SH → S + OH) on the quartet surface appears as a minor channel at high temperatures.