Measurement of the Intramolecular Hydrogen-Shift Rate Coefficient for the CH3SCH2OO Radical between 314 and 433 K

The intramolecular hydrogen-shift rate coefficient of the CH3SCH2O2 (methylthiomethylperoxy, MSP) radical, a product formed in the oxidation of dimethyl sulfide (DMS), was measured using a pulsed laser photolysis flow tube reactor coupled to a high-resolution time-of-flight chemical ionization mass spectrometer that measured the formation of the DMS degradation end product HOOCH2SCHO (hydroperoxymethyl thioformate). Measurements performed over the temperature range of 314–433 K yielded a hydrogen-shift rate coefficient of k 1(T) = (2.39 ± 0.7) × 109 exp(−(7278 ± 99)/T) s–1 Arrhenius expression and a value extrapolated to 298 K of 0.06 s–1. The potential energy surface and the rate coefficient have also been theoretically investigated using density functional theory at the M06-2X/aug-cc-pVTZ level combined with approximate CCSD­(T)/CBS energies yielding k 1(273–433 K) = 2.4 × 1011 × exp­(−8782/T) s–1 and k 1(298 K) = 0.037 s–1 in fair agreement with the experimental results. Present results are compared with the previously reported values of k 1(293–298 K).