The photodissociation of ClO2: Potential energy surfaces of OClO->Cl+O-2

Using large multireference configuration interaction wave functions, potential energy surfaces involved in the photodissociation of symmetric ClO2 to Cl+O-2 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(2)B(2) electronic state after initial excitation to the A (2)A(2) state. A calculated C-2 upsilon transition state connecting 1 B-2(2) OClO to Cl+0(2), is strongly bent and has a barrier height relative to the X B-2(1) 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+O-2 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+O-2 will be formed in the photodissociation of ClO2 due to the dominance of the ClO+O channel, Much of the O-2 that is produced is predicted to be in the a (1) Delta(g) state, since the 1 B-2(2) potential energy surface in C-2v symmetry correlates with this state of O-2. However, other nearby electronic states of OClO, namely the 1 (2)A(1) and 2 B-2(2), interact in the exit channel and will facilitate the production of especially X (3) Sigma(g)(-) and perhaps b (1) Sigma(g)(+) O-2, 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)]. (C) 1996 American Institute of Physics.