Na2O and Na2O+: Thermodynamics and low-lying electronic states

High-level [up to RCCSD(T)/aug-cc-pV5S'//RCCSD/aug-cc-pVQZ'] ab initio calc ulations are performed on Na2O and Na2O+ (where the 'indicates a nonstandar d aug-cc-pVXZ basis set). The electronic groundstate equilibrium geometries are found to be linear in both cases. The heats of formation, Delta H-f(29 8)(Na2O) and Delta Hf-298(Na2O+), are derived, with the recommended values being Delta H-f(298)(Na2O) = -5.5 +/- 1.0 kcal mol(-1) and Delta H-f(298)(N a2O+) = 106.7 +/- 0.5 kcal mol(-1), respectively. It is found that large ba sis sets, the RCCSD(T) method, and appropriate account of basis set superpo sition error (BSSE) are necessary in order to obtain reliable results. S-29 8 for Na2O and Na2O+ are also calculated giving 67 and 63 cal K-1 mol(-1), respectively. The calculations also yield Delta H-a(298)(Na2O)= 115.5 +/- 1 kcal mol(-1) and Do(NaO Na) = 52 +/- 1 kcal mol(-1) The adiabatic ionizati on energy of Na2O is calculated as 4.86 +/- 0.02 eV and corresponds to the process Na2O+((XIIu)-I-2) + e(-) <-- Na2O(X(1)Sigma(g)(divided by)); the co rresponding vertical ionization energy is calculated to be 5.00 +/- 0.02 eV . The ground state of Na2O+ is established as the (IIu)-I-2 state, with the A(2)Sigma(u)(+) state lying ca. 0.65 eV above. The low:lying triplet state s of Na2O are briefly considered. The implication of the present results on the mass spectrometry of the vapor above Na2O is discussed.