Theoretical and Thermochemical Network Approaches To Determine the Heats of Formation for HO2 and Its Ionic Counterparts

The purpose of this study is to give reliable and accurate thermochemical data for HO2, HO2+, and HO2–. Their heats of formation were determined using quantum chemical calculations with the aid of high-accuracy coupled-cluster methods taking account of zero-point vibrational energies, scalar-relativistic effects, and the deficiencies of the Born–Oppenheimer approximation. Furthermore, a thermochemical network, containing 14 experimental and 7 theoretical reaction enthalpies, was set up to determine even more accurate heats of formation. The iteratively reweighted least-squares solution of the network yielded the best heat of formation estimates, which are ΔfH0°(HO2) = 14.85 ± 0.22, ΔfH298°(HO2) = 11.92 ± 0.22, ΔfH0°(HO2+) = 1110.56 ± 0.40, ΔfH298°(HO2+) = 1107.64 ± 0.40, ΔfH0°(HO2–) = −89.04 ± 0. 39, and ΔfH298°(HO2–) = −91.75 ± 0.39 kJ/mol. In addition, in line with previous accurate data ΔfH0°(OH) = 37.25 ± 0.03, ΔfH0°(OH+) = 1293.20 ± 0.03, and ΔfH0°(H2O2) = −129.48 ± 0.06 kJ/mol were also delivered by our network.