Does chlorine peroxide exhibit a strong ultraviolet absorption near 250 nm?

A theoretical investigation of the low-lying singlet electronic states of chlorine peroxide (ClOOCl) is presented. Calculations of excitation energies and oscillator strengths at the equation of motion coupled-cluster singles and doubles level predict that six excited states of ClOOCl are accessible at photon wavelengths above 200 nm. These states occur in three sets of pairs which can be approximately represented as symmetrized and antisymmetrized excitations of electrons from lone pair and Cl–O bonding orbitals to antibonding Cl–O orbitals. While small oscillator strengths are predicted for transitions to the lowest two ‘‘pairs’’ of states, sizable values are predicted for the X 1A→E 1A and X 1A→F 1B transitions (0.02 and 0.08, respectively). Furthermore, our estimation of the vertical excitation energy for these processes is ≊5.20 eV, in satisfactory agreement with the experimentally observed band maximum of ClOOCl at 5.04 eV. The results of this work lend strong support to the contention that photodissociation of ClOOCl plays an important role in the catalytic destruction of stratospheric ozone.