| Abstract
| - A theoretical study of the low-lying singlet and triplet states of ClONO is presented. Calculations of excitationenergies and oscillator strengths are reported using multireference configuration interaction, MRD-CI, methodswith the cc-pVDZ + sp basis set. The calculations predict the dominant transition, 4A‘ ← 11A‘, at 5.70 eV.The transition 21A‘ ← 11A‘, at 4.44 eV, with much lower intensity nicely matches the experimental absorptionmaximum observed around 290 nm (4.27 eV). The potential energy curves for both states are found to behighly repulsive along the Cl−O coordinate implying that direct and fast dissociation to the Cl + NO2 productswill occur. Photodissociation along the N−O coordinate is less likely because of barriers on the order of 0.3eV for low-lying excited states. A comparison between the calculated electronic energies related to the twodominant excited states of ClONO and BrONO indicates that the transitions lie about 0.6 eV higher if bromineis replaced by chlorine. The stratospheric chemistry implications of ClONO and BrONO are discussed.
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