Laser investigation of decay dynamics in superexcited Rydberg states of NO

Superexcited Rydberg states (n = 7-45, l = s, p, and f, v = 0, 1) of NO have been state-selectively produced with a two-color double resonance excitation method, and fragment atoms produced by predissociation and NO⁺ ions generated by autoionization have been directly detected by a resonance enhanced multiphoton ionization technique. As a result, not only N(²D)-generating predissociation predicted by previous studies has been confirmed, but unexpected generation of N(⁴S) has also been observed. Competition between vibrational autoionization and predissociation shows strong dependence on the orbital angular momentum and principal quantum number. Striking rotational state dependence of the decay dynamics in the superexcited 7f state (v = 1) has been found. Through detailed analysis, it has been shown that the decay dynamics of the 7f state (v = 1) is governed by predissociation processes due to direct coupling with Σ⁺ valence states. Furthermore, studying the competition between rotational autoionization and predissociation, it has also been demonstrated that the decay dynamics of the rotational superexcited states are predominantly governed by predissociation, not by rotational autoionization.