All-valence-electron CI study of the ground and lowest excited states of the hydroperoxyl radical

Ab initio calculations using a double-zeta plus polarization AO basis are used to study the lowest-lying (²A′ ← ²A″) transition of the HO₂ radical. A large-scale CI treatment is found to result in a transition energy for this system which agrees to within less than 0.1 eV with its experimental value. The life-time of the process is predicted to be in the order of 3 × 10^?3 s using the dipole length formula for this quantity, while the generally less reliable dipole velocity result is found to be several orders of magnitude larger.