Imaging fast relaxation dynamics of NO2

Time-resolved spectroscopy combined with velocity map imaging techniques have been used to investigate the multiphoton dynamics of the NO2 molecule. Two different pump-probe excitation schemes were used to explore different potential energy surfaces (PESs) located in the first dissociation region and in the Rydberg region around 9.2 eV. Integrated and energy-resolved signals of NO2+, NO+ and photoelectrons were recorded as a function of time. When exciting with 403 nm photons, the NO+ signal exhibits an intriguing oscillatory behaviour with a period of 512 fs. The NO+ and photoelectron kinetic energy distributions produced by this pump wavelength were cold, while those produced when employing 269 nm photons as pump were very rich, evidencing the presence of multiple excitation channels. A couple of sharp long-lived photoion-photoelectron peaks represents the most salient feature of the latter. They were assigned to an excitation by two 269 nm photons to a Rydberg state dissociating into NO(A(2)Sigma(+)) + O(P-3). This NO+ peak as well as another one located at 0 eV display very complex time dependencies including the signatures of two dissociation dynamics on timescales of 400 and 600 fs. The different pathways responsible for this temporal behaviour are discussed in view of shedding light onto the underlying multichannel multiphoton dynamics.