Multiresonant spectroscopy and dynamics of molecular extravalent states: State-resolved intramolecular relaxation of NO2 above 9 eV

Multiresonant methods are described for the optical selection of individual rovibrational states at energies near and above the first ionization threshold of NO 2 . These techniques are applied to resolve distinct Rydberg series converging to respective vertical ionization potentials by optical absorption from assigned vibration-rotation levels of the low-lying sharp 3pσ 2 Σ u + state. Spectra of levels lying between adiabatic and vertical thresholds show evidence for vibrational autoionization. This process is found to be comparatively slow ( T ⪢ 30 ps) for all levels but those for which autoionization via a Δν=−1 transition in the symmetric stretch, ν 1 , is accessible. Such rates are fastest for levels just above this Δν=−1 threshold, exhibiting characteristic Fano lineshapes as broad as 11 cm −1 . Bands thereupon proceed to narrow with increasing energy, to first re-exhibit rotational fine structure, then evidence l uncoupling in patterns of transitions very close to vertical thresholds.