A realistic multi-sheeted potential energy surface for NO_2~(2A') from the double many-body expansion method and a novel multiple energy-switching scheme

摘要

We report a new multi-sheeted double many-body expansion energy surface that reproduces most known topological features of the title system. Near spectroscopic accuracy is conveyed to the grond-state sheet of ~2A_1 (1 ~2A' in C_s) symmetry in the vicinity of the minimum b merging it with a spectroscopically determined Taylor-series-expansion-type form via a novel multiple energy-switching scheme. A high energy ridge for C_2v insertion of N(~4S) into O_2(X~3EPSILON_g~-) has also been imposed to mimic the resutl of accurate ab initio complete active space self-consistent field and second-order perturbation theory on CAS wave function calculations carried out for such geometries. This ridge decreases for C_s geometries yielding a minimum barrier height for the N + O_2 reaction of 0.273 eV at a bent N-O-O structure defined by R_NO = 3.107a_o, R_OO = 2.513a_O, and angleNOO = 113.5 deg. Both the location and height of this barrier are in good agreement with existing ab initio calculations and the recommended values. Another salient feature is a shallow minimum on the A ~2B_2 potential energy surface that is separated from the absolute X ~2A_1 minimum by a conical intersection. Such a feature is accurately predicted by the newly reported ab initio calculations and well mimicked by the global double many-body expansion/energy-switching potential energy surface here reported. This is therefore commended both for spectrsocopic and reactive dynamics studies on the title system. A final comment in relation to the conical intersection and the energy-switching scheme goes to the expected accuracy of current approaches for spectroscopicall determined effective single-valued forms.