Theoretical investigation on the reaction mechanism of ozone with chlorine, bromine and iodine atoms

Abstract

Theoretical investigation on the reaction mechanism of X + O3 → XO + O2 (X = Cl, Br and I) reactions have been performed at the ab initio level using correlation consistent and effective core potential basis sets. The geometry and frequency of the reactants, products, equilibrium geometries and transition states are obtained using MP2 level of theory and energetics are calculated at the CCSD(T) and QCISD(T) methods. Heat of reactions are found to be consistent with the experimental data. Possible reaction pathways are discussed. In case of reactions of ozone with chlorine and brome, it starts producing a nonplanar trioxide (OOOX) transition state with acute dihedral angle. It then proceeds via nonplanar equilibrium geometry and transition state. Finally dissociates to XO + O2 from a planar O2·OX equilibrium geometry. For the reaction with iodine, initial transition state and equilibrium geometry with acute dihedral angle are disappeared. The reaction proceeds through planar intermediates and finally dissociated to IO + O2 via O2·OI isomer. There exists a flat plateau on the potential energy surface in the intermediate region for all the cases. Finding of O2·OX equilibrium geometry strengthens the suggestion of previous investigations and for the possibility of direct reaction mechanism. High level theoretical investigation including reaction dynamics on these reactions can reveal the actual reaction mechanism.