Laser induced dispersed fluorescence spectroscopy of 107 vibronic levels of NO2 ranging from 12 000 to 17 600 cm−1

Abstract

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, X̃ 2A1, and the isoenergetic levels of the electronic excited state, à 2B2. 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 à 2B2 and the low-lying vibrational levels of X̃ 2A1. This means that the vibronic interactions occurring between the vibrational levels of X̃ 2A1 and à 2B2 are not strong enough to systematically mix together several bright parent states of à 2B2. 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.