AB-INITIO STUDY OF NO2 .6. VIBRATIONAL AND VIBRONIC COUPLING IN THE (X)OVER-TILDE(2)A(1) (A)OVER-TILDE(2)B(2) 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 (X) over til de(2)A(1)/(A) over tilde(2)B(2) conical intersection spectrum of NO2. By analyzing the expansion coefficients of the nonadiabatic states, we have discussed the (X) over tilde(2)A(1) vibrational resonances above 4600 cm(-1) and the interplay among the (X) over tilde(2)A(1) vibrati onal and (X) over tilde(2)A(1)/(A) over tilde(2)B(2) vibronic coupling s in the energy range 8900-12 000 cm(-1). The assignment and the vibra tional 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 (A) over tilde(2)B(2) vibra tional bands has extended our previous assignment and has shown that F ermi, Darling-Dennison. and two new (A) over tilde(2)B(2) vibrational resonances contribute to several nonadiabatic states above 12 000 cm(- 1). We have finally reported the (A) over tilde(2)B(2) vibrational ban ds up to 16 000 cm(-1) and the corresponding clusters of nonadiabatic levels, which have been compared with some experimental results. (C) 1 997 American Institute of Physics.