The heat of formation of NaO2+(X 3Σ−) and NaO2(X̃ 2A2)

High-level ab initio calculations are performed to calculate the global minimum energy structure for NaO2+. At the RCCSD/aug-cc-pV5Z//RCCSD(T)/aug-cc-pVQZ(no g) level of theory it is found that the global minimum is the linear Na–O–O (X 3Σ−) state; a C2v (3B1) structure lies 800 cm−1 above this. ΔHf298[NaO2+(X 3Σ−)] is calculated to be 139.5±2 kcal mol−1, with a dissociation energy, D0(Na+⋯O2)=4.6±0.3 kcal mol−1. ΔHf298[NaO2(X̃ 2A2)] is derived as −13±3 kcal mol−1, and D0(Na⋯O2)=36±3 kcal mol−1. The adiabatic ionization energy, for the process NaO2+(X 3Σ−)) ← NaO2(X̃ 2A2) is calculated to be 6.47±0.03 eV.