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

The energy of CH3SOO. relative to CH3S. + O-3(2) is calculated within both a DFT formalism and a configuration interaction treatment (MRSDQCI). The fo und stabilisation of CH3SOO., 38.4 kJ mol(-1) (DFT) and 61.9 kJ mol(-1) (MR SDQCI level), agrees well with an experimental value of 48.9 kJ mol(-1). Th e reactive pathway for the addition of O-3(2), to CH3S. has no activation b arrier within the interaction configuration treatment. These theoretical re sults further substantiate the experimental observations, in the gas phase as well as in solution, of an equilibrium between CH3S. + O-3(2) and (CHSOO .)-S-3. The electronic structure of the complex CH3SOO. is discussed. The U V spectrum of CH3SOO. has been calculated within the MRSDQCI method: contra ry to previous calculations, several high-wavelength transitions are expect ed. 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. Sev illa [J. Phys. Chem. 99 (1995) 7993] to an excitation from the sulphur lone pair to the SOMO, mostly localised on the terminal oxygen. (C) 1999 Elsevi er Science B.V. All rights reserved.