Structure and predissociation dynamics of electronically excited nitrogen dioxide: A resonance Raman study

Resonance Raman spectra of NO2 have been recorded as a function of excitation frequency in the range 0--8000 cm-1 above the predissociation threshold. These spectra are interpreted using the time-dependent formulation of resonant Raman scattering, to elucidate the shape of the excited electronic state potential energy surface, and the dynamics which occur on it immediately following photoexcitation. Our results show that the dominant optical transition in this spectral range is 2B2--2A1. Our Raman spectra reveal a marked decrease in the dynamical time scale of the predissociation of the 2B2 state as excitation frequency increases. At excitation frequencies approximately 4850 cm-1 above the dissociation threshold, the 2B2 predissociative lifetime becomes comparable to a vibrational period. We have analyzed the resonance Raman spectra, along with the absorption spectrum, to determine the magnitudes of the slopes of the potential surface along the symmetric stretch and bending normal coordinates for the 2B2 excited state in the Frank--Condon region