Global ab Initio Potential Energy Surfaces for Low-Lying Doublet States of NO3

We report analytical global potential energy surfaces (PESs) for three low-lying doublet states (D-0, D-1, and D-2) of NO3. The fits are made on roughly 74000 MS-CAS(17e,13o)PT2/aug-cc-pVTZ calculations of electronic energies, where these PESs are invariant of permutations of oxygen atoms. The surfaces describe two roaming pathways for NO3 -> NO2-O -> NO + O-2 involving different electronic states discovered in the photolysis of NO3 [Xiao, H. Y. et al. J Phys. Chem. Lett 2011, 2, 934]. These pathways become accessible at excess energy of similar to 210 kJ/mol above the ground-state global minimum of NO3. The ab initio data below 360 kJ/mol are reproduced very well by the fitted PESs with the fitting rms errors of less than 5.5 kJ/mol for all the three states. Moreover, key local minima and energy profiles along the roaming pathways on the fitted PESs are compared with those on the ab initio PESs. In addition, potential contour maps in the roaming region are also compared These careful evaluations of the fitted PESs suggest that the present fitted PESs are well suited for future dynamics calculations of this system.