Multiresonant spectroscopy and dynamics of molecular extravalent states: State-resolved intramolecular relaxation of NO 2 above 9 eV

Abstract

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 2Σ 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.