The heat of formation of NaO2+(X-3 Sigma(-)) and NaO2((X)over-tilde(2)A(2))

High-level ab initio calculations are performed to calculate the global min imum energy structure for NaO:. At the RCCSD/aug-cc-pV5Z//RCCSD(T)/aug-cc-p VQZ(no g) level of theory it is found that the global minimum is the linear Na-O-O (X(3)Sigma(-)) state; a C-2v (B-3(1)) structure lies 800 cm(-1) abo ve this. Delta H-f(298)[NaO2+(X(3)Sigma(-))] is calculated to be 139.5 +/- 2 kcal mol(-1), with a dissociation energy, Do(Na+... O-2) = 4.6 +/- 0.3 kc al mol(-1). H-f(298)[NaO2((X) over tilde(2)A(2))] is derived as -13 +/- 3 k cal mol(-1), and D-0(Na ... O-2) = 4.6 +/- 0.3 kcal mol(-1). The adiabatic ionization energy, for the process NaO2+(X(3)Sigma(-))) <-- NaO2((X) over t ilde(2)A(2)) is calculated to be 6.47 +/- 0.03 eV. (C) 1999 Elsevier Scienc e B.V. All rights reserved.