A theoretical study of the low-lying excited states of ozone

Abstract

A theoretical study has been performed on the five lowest excited states of the ozone molecule using multiconfigurational second-order perturbation theory (CASPT2). The predicted order of states is: 3A 2 ( T 0 = 1.15 eV), 3B 2 ( T 0 = 1.33 eV, 3B 1 ( T 0 = 1.33 eV), 1A 2 ( T 0 = 1.44 eV) and 1B 1 ( T 0 = 1.88 eV). Corresponding experimental data are: 1.18, 1.30, 1.45, 1.58, and 2.05 eV, respectively. Equilibrium geometries, harmonic frequencies of symmetric vibrations, and vertical excitation energies are also reported. The dissociation limit D e for the ground state of ozone is found to be 1.08 eV, in agreement with the experimental value (1.13 eV). The calculations make use of a modified Fock operator in the CASPT2 theory. Relative energies of states with a different number of open shells are substantially improved. The modified CASPT2 method was checked by calculating spectroscopic constants of the oxygen molecule.