SPECTROSCOPY AND THERMODYNAMICS OF NAO-3-SIGMA(-)) - RELEVANCE TO ATMOSPHERIC CHEMISTRY((X)

The spectroscopy and thermodynamics of the atmospherically important N aO+(X(3)Sigma(-)) species are calculated using high-level ab initio ca lculations, up to the RCCSD(T)/aug-cc-pVSZ level. The calculated disso ciation energy was Do 0.29 +/- 0.02 eV, which is to the low end of the range of values obtained from previous experimental studies. This low er value for the dissociation energy of NaO+ has implications for expe rimental values of the dissociation energy of NaO and the adiabatic io nization energy (AIE) of NaO. Further calculations led to the dissocia tion energy of NaO(X(2)Pi) being calculated as D-0 = 2.71 +/- 0.07 eV, with the AIE for the NaO+(X(3)Sigma(-)) <-- NaO(X(2)Pi) ionization be ing calculated as 7.55 +/- 0.08 eV. The dissociation energy of NaO is to the high end of previous experimental determinations but agrees ver y well with previous ab initio calculations. The AIE is somewhat highe r than the onset measured in a recent photoelectron experiment, and th is is discussed. In addition, a potential energy curve and dipole mome nt function for NaO+(X(3)Sigma(-)) are calculated at the RCCSD(T)/aug- cc-pVQZ level. From the potential energy curve, vibrational separation s and rotational energy levels were calculated, and from the calculate d rovibrational levels, thermodynamic quantities were derived. The low -energy region of the NaO(X(2)Pi) potential energy curve is also calcu lated, allowing the lowest energy levels to be obtained. From the vibr ational wave functions of the neutral and cationic states, Franck-Cond on factors were calculated for the first photoelectron band, which cor responds to the NaO+(X(3)Sigma(-)) <-- NaO(X(2)Pi) ionization. The rol e of NaO+ in atmospheric chemistry is discussed as well as the implica tions the present results have on a recently suggested model for the f ormation of sporadic sodium layers. It is noted that the a(1)Delta sta te, of NaO+ will be metastable and so may have a role in atmospheric c hemistry.