The thiyl peroxyl radical: formation and UV spectrum. A multiconfigurational ab initio study Original Research Article

The energy of CH3SOO⋅ relative to CH3S⋅+3O2 is calculated within both a DFT formalism and a configuration interaction treatment (MRSDQCI). The found stabilisation of CH3SOO⋅, 38.4 kJ mol−1 (DFT) and 61.9 kJ mol−1 (MRSDQCI level), agrees well with an experimental value of 48.9 kJ mol−1. The reactive pathway for the addition of 3O2 to CH3S⋅ has no activation barrier within the interaction configuration treatment. These theoretical results further substantiate the experimental observations, in the gas phase as well as in solution, of an equilibrium between CH3S⋅+3O2 and CH3SOO⋅. The electronic structure of the complex CH3SOO⋅ is discussed. The UV spectrum of CH3SOO⋅ has been calculated within the MRSDQCI method: contrary to previous calculations, several high-wavelength transitions are expected. One of them is calculated at 536 nm, for experimental values around 540 nm, and corresponds as inferred by Y. Razskazovskii, A.O. Colson, M.D. Sevilla [J. Phys. Chem. 99 (1995) 7993] to an excitation from the sulphur lone pair to the SOMO, mostly localised on the terminal oxygen.