High Energy States of Ozone Obtained from New Ab Initio Potential Energy Surfaces and from Experimental Spectra Analyses: the “Reef Structure” Puzzle

High-energy states of ozone ¹⁶O₃ and ¹⁸O₃ isotopologues were predicted from a new ab initio potential energy surface¹ and derived from experimental spectra analysis up to 7920 cm⁻¹. A brief outline is given for highly accurate ab initio² calculations and for new analytical PES modeling. The new analytical PES of ozone takes into account such structural properties of ozone as non-linear minimum energy path and non-additivity of the fragmentation energy. The ”reef structure” (activation barrier) problem is investigated as well as its influence on the shifting of harmonic frequencies and vibrational energy levels of ozone. Correction of ab initio data was made by accounting for the couplings of many excited electronic states³. It is shown that this correction leads to a smoother PES with the ”reef structure” almost vanishing. The PES ”without reef structure” appears to be more precise in terms of spectroscopy: vibration energies are in good agreement with available experimental data^4,5,6 up to 94% of the dissociation energy with an average error of vibrational prediction near 1 cm⁻¹, which is much better than all available calculations that involve the activation barrier on the transition state.