Autoionization widths of the NO Rydberg-valence state complex in the 11–12 eV region

The photoion excitation spectra of 14NO and 15NO have been studied in the 105–112 excitation region using high-order harmonic laser spectroscopy. Utilizing the small bandwidth offered by this technique, the natural widths of prominent lines in this region have been measured. These lines originate from interactions between high-lying Rydberg levels converging to the NO+ electronic ground state and a ‘new’ NO valence state situated close to the latter state. The present measurements show broad resonances corresponding to a decay time of 20–50 fs. This supports the interpretation that the decay takes place via rapid electronic autoionization.