Structure of isolated and solvated peroxyl radicals

We have investigated the structure of HO2, and a series of alkyl peroxyl ra dicals ROO using a variety of quantum mechanical methods. We first compute the geometries, vibrational frequencies, electronic charge distributions, a nd spin densities for the series of radicals considered in the gas phase. S ignificant differences with respect to previous calculations have been poin ted out in a few cases. In particular, we show the fundamental importance o f electronic correlation when computing net atomic charges and spin densiti es, which have generally been estimated in the litterature by means of Hart ree-Fock SCF electronic densities. Solvation effects on the geometry and el ectronic structure have been estimated by carrying out self-consistent reac tion field computations in a polarizable continuum environment with relativ e dielectric permittivity equal to that of liquid water. Large electronic p olarization is predicted in such conditions. This may be important in order to understand reactive properties of the radicals in different media. (C) 1999 John Wiley & Sons, Inc.