An ab initio molecular orbital study of the electronically excited and cationic states of the ozone molecule and a comparison with spectral data

Abstract

A number of valence and Rydberg, singlet and triplet excited states for ozone in the excitation energy range 1–12eV have been calculated by large scale CI methods preceded by MCSCF studies. A comparison of the theoretical intensity envelope with the VUV + EELS spectrum has been made. The present work supports the assignments for the Huggins + Hartley bands as having two electronic origins, 2 ¹A₁ and 1 ¹B₂. The experimental ∼ 9.3eV and ∼ 10.2eV bands of the VUV spectrum must have adventitious superposition of valence states on Rydberg transitions, because the high oscillator strengths of the valence states cannot be attributed to the 8.8eV broad band. A number of new valence and Rydberg states have been calculated, and these lead to the conclusion that the experimental 9–11 eV VUV spectral range in particular must yield more experimental states than the few so far identified. This suggests a major need for more sophisticated methods of experimental study for the excited state manifolds. The use of various MCSCF/CI studies of the vertical cationic states, supports the IP order as ²A₁ < ²B₂ < ²A₂. A re-analysis of the 12–13.4eV range of the UV-photoelectron band has been performed, with a view to determining the adiabatic IPs more accurately. The present work suggests that the adiabatic IP₂ lies at 12.86eV, slightly lower than has been assumed, with consequential effect on the analysis of the VUV spectrum near 9.4eV.