Laser spectroscopic investigation of high Rydberg states of NO: Decay dynamics near the first ionization threshold

With a state-selective laser excitation, two main decay processes, autoionization and predissociation, in vibrational superexcited Rydberg states (n = 8-12, l = s, p, and f, v = 1) of NO have been studied, directly detecting not only NO⁺ ions generated by autoionization but also every fragment atom produced by predissociation. In addition, the v = 0 states lying below the ionization threshold have also been investigated with the same method, and the comparison between the two results has more clearly elucidated the competing behavior of the decay processes in the above-threshold states (v = 1). As a result, for the v = 1 state, it has been shown that predissociation is the main decay process in the np Rydberg states, while autoionization is dominant in the ns Rydberg states. For the nf Rydberg states, the N(⁴S)+O(³P) predissociation channel, which has not been emphasized in previous studies, has been found to play an important role in the decay dynamics both above and below the ionization threshold.