Laser induced dispersed fluorescence spectroscopy of 107 vibronic levels of NO2 ranging from 12000 to 17600 cm(-1)

We report the laser induced dispersed fluorescence spectra (LIDFS) of NO2 recorded when exciting 107 vibronic;levels lying between 11 961 and 17 627 cm(-1). These levels result from the vibronic interactions between the highly excited vibrational levels of the electronic ground state, (X) over tilde (2)A(1), and the isoenergetic levels of the electronic excited state, (A) over tilde B-2(2). One observes that the intensity patterns of almost half of the LIDFS can be interpreted in terms of Franck-Condon factors (FCFs) between a single bright parent level belonging to (A) over tilde B-2(2) and the low-lying vibrational levels of (X) over tilde (2)A(1). This means that the vibronic interactions occurring between the vibrational levels of (X) over tilde (2)A(1) and (A) over tilde B-2(2) are not strong enough to systematically mix together several bright parent states of (A) over tilde B-2(2). We have also found that vibronic eigenstates scattering over several hundreds of cm(-1) can be assigned to the same bright parent state. However, these features, which are characteristic of individual vibronic levels, must be faced with the statistical properties of the NO2 visible spectrum, well-known to exemplify molecular quantum chaos, at least above 16 500 cm(-1) [J. Chem. Phys. 103, 1732 (1995)]. Complementarily, we briefly present results of the breakdown of vibrational and rotational selection rules, as observed in LIDFS. This phenomenon reflects the onset of strong vibronic and rovibronic interactions that progressively destroy the above mentioned one-bright-parent-state model and leads, at higher energies, to a regime of rovibronic chaos. (C) 2001 American Institute of Physics.