ON THE ENERGY SEPARATION BETWEEN THE OPEN AND CYCLIC FORMS OF OZONE

The equilibrium structure of the D3h form of ozone has been determined using large atomic natural orbital (ANO) basis sets in conjunction with the singles and doubles coupled-cluster (CCSD) and CCSD(T) ab initio models of electron correlation. The largest one-particle basis sets include g-type functions. In addition, harmonic vibrational frequencies have been determined. The results allow a very accurate determination of the energy difference (ΔE) between the open and cyclic forms of ozone. The highest level of theory used gives a ΔE of 29.1 kcal/mol, of which triple excitations contribute 5.8 kcal/mol. Zero-point vibrational energies decrease ΔE by 0.4 kcal/mol, yielding a final estimate of 28.7 kcal/mol. These results demonstrate that cyclic ozone is above the O3(X1A1)→O(3P)+O2(X3Σg-) dissociation limit (26.1 kcal/mol). © 1990.