Ab initio study of NO2. VI. Vibrational and vibronic coupling in the X2A1/Ã2B2 conical intersection up to 16 000 cm−1

Following our previous work [J. Chem. Phys. 105, 9051 (1996)], we have investigated the vibrational and vibronic mixings in the X̃2A1/Ã2B2 conical intersection spectrum of NO2. By analyzing the expansion coefficients of the nonadiabatic states, we have discussed the X̃2A1 vibrational resonances above 4600 cm−1 and the interplay among the X̃2A1 vibrational and X̃2A1/Ã2B2 vibronic couplings in the energy range 8900–12 000 cm−1. The assignment and the vibrational mixing of the nonadiabatic bands have been studied by comparing two-dimensional contour plots of Born–Oppenheimer and of generalized vibrational functions. A Dunham fit to the Ã2B2 vibrational bands has extended our previous assignment and has shown that Fermi, Darling–Dennison, and two new Ã2B2 vibrational resonances contribute to several nonadiabatic states above 12 000 cm−1. We have finally reported the Ã2B2 vibrational bands up to 16 000 cm−1 and the corresponding clusters of nonadiabatic levels, which have been compared with some experimental results.