Stationary points on the energy hypersurface of the reaction O3+H• → [•O3H]* ⇆ O2+•OH and thermodynamic functions of •O3H at G3MP2B3, CCSD(T)-CBS (W1U) and MR-ACPF-CBS levels of theory

The relative enthalpies, Delta H degrees (0) and Delta H degrees (298.15), of stationary points (four minimum and three transition structures) on the (O3H)-O-center dot potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)-CBS (W1U) procedures from which we earlier found mean absolute deviations (MAD) of 3.9 kJ mol(-1) and 2.3 kJ mol(-1), respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For CCSD(T)-CBS (W1U) the well depth from O-3 + H-center dot to trans-(O3H)-O-center dot, Delta H degrees(well)(298.15) = -339.1 kJ mol(-1), as well as the reaction enthalpy of the overall reaction O-3 + H-center dot -> O-2 + (OH)-O-center dot, Delta(r)H degrees(298.15) = -333.7 kJ mol(-1), and the barrier of bond dissociation of trans-(O3H)-O-center dot -> O-2 + center dot OH, Delta H degrees(298.15) = 22.3 kJ mol(-1), affirm the stable short-lived intermediate (O3H)-O-center dot. In addition, for radicals cis-(O3H)-O-center dot and trans-(O3H)-O-center dot, the thermodynamic functions heat capacity C degrees(p) (T), entropy S degrees ( T), and thermal energy content H degrees(T)-H degrees(0) are tabulated in the range of 100 - 3000 K. The much debated calculated standard enthalpy of the formation of the trans-center dot O3H resulted to be Delta(f)H degrees(298.15) = 31.1 kJ mol(-1) and 32.9 kJ mol(-1), at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied to consider possible multiconfiguration effects and yield Delta(f)H degrees(298.15) = 21.2 kJ mol(-1). The discrepancy between calculated values and the experimental value of -4.2 +/- 21 kJ mol(-1) is still unresolved.