The photodissociation of ClO2: Potential energy surfaces of OClO→Cl+O2

Abstract

Using large multireference configuration interaction wave functions, potential energy surfaces involved in the photodissociation of symmetric ClO2 to Cl+O2 are investigated. The production of atomic chlorine from OClO, which may have important implications for stratospheric ozone chemistry, is predicted to occur via the excited 1 2B2 electronic state after initial excitation to the A 2A2 state. A calculated C2v transition state connecting 1 2B2 OClO to Cl+O2 is strongly bent and has a barrier height relative to the X 2B1 ground state of 2.86 eV (2.75 eV with zero-point vibrational corrections). However, this is only a 2nd-order transition state with imaginary vibrational frequencies along both the OClO→Cl+O2 and OClO→ClO+O reaction paths (symmetric bending and asymmetric stretching modes, respectively). Thus, the present theoretical work suggests that only a small amount of Cl+O2 will be formed in the photodissociation of ClO2 due to the dominance of the ClO+O channel. Much of the O2 that is produced is predicted to be in the a 1Δg state, since the 1 2B2 potential energy surface in C2v symmetry correlates with this state of O2. However, other nearby electronic states of OClO, namely the 1 2A1 and 2 2B2, interact in the exit channel and will facilitate the production of especially X 3Σ−g and perhaps b 1Σ+g O2, respectively. The present results are in very good accord with the recent photofragment translational energy spectroscopy experiments of Davis and Lee [J. Chem. Phys. 105, 8142 (1996)].