Nonadiabatic radiative lifetimes and fluorescence spectra of NO2

We have computed the radiative lifetimes and fluorescence spectra of the B-2 nonadiabatic states of NO2 up to 18 735 cm(-1), employing ab initio MRD-CI potentials refined with respect to the experimental lines up to 10 000 cm(-1). The effects of the conical intersection (X) over tilde(2)A'/(A) over tilde(2)A' between the first two adiabatic surfaces on the radiative lifetimes have been investigated by comparing the lifetimes of the nonadiabatic states with those of vibrational states of the excited electronic species. By this way we have confirmed that the anomalous long lifetimes observed for NO2 are caused by the nonadiabatic couplings, suggesting furthermore that the lifetimes of some weak absorbing states are on the contrary lowered by the conical intersection. We have compared our lifetimes with the published experimental measurements, showing that we are able to well reproduce and explain the general experimental trends and that the computed results agree with the experimental ones within a factor two or three. These differences are similar to those found among the observed lifetimes. Moreover, we have computed laser induced fluorescence spectra and compared them with the experimental ones, showing a fair agreement in the low-energy range 11 600-13 900 cm(-1) and a rough agreement in the high-energy range 16 000-18 735 cm(-1), and suggesting the assignments for the main 1(2)B(2) characters of some strongest bands. Finally, we have computed dispersed fluorescence spectra for some initial states, by pointing out that they can be very different because of the difference of the wave functions of the initial states. (C) 1999 American Institute of Physics. [S0021-9606(99)30541-9].