Laser Spectroscopic Investigation of High Rydberg States of no: Decay Dynamics Near the First Ionization Threshold

Asuka Fujii,Norio Morita

doi:10.1155/1994/49739

Abstract

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.

Highlights

The first ionization threshold, there are still many neutral states
We investigated the decay dynamics of high Rydberg states around the first ionization threshold of NO with a laser spectroscopic method
The rotational levels of the ns, np, and nf Rydberg states are assigned to the N I(R 1), N I(R 0), and N I(R 2) levels, respectively, where R is a total angular momentum of the ion-core

Summary

INTRODUCTION

The first ionization threshold, there are still many neutral states. These molecular states are called superexcited states, and have been considered to make important contribution to various chemical reactions. 1,2 One example of such states is a high Rydberg state having a vibrationally excited ion core. In this type of states, which will be called a superexcited Rydberg state hereafter, one of the main decay processes is autoionization, in which vibrational energy of the ion core is converted to electronic energy Another important decay process in highly excited states is predissociation, and the competition between these two processes is the central subject in the dynamics of superexcited states. The competition between vibrational autoionization and predissociation showed strong dependence on the orbital angular momentum and principal quantum number In addition to these measurements on superexcited Rydberg states, we observed decay processes of the v 0 levels as well. These levels lie below the first ionization threshold, and their autoionization channels are closed. The comparison between dynamical behaviors of the v 0 and 1 levels allowed us more clearly to understand the complicated dynamical behavior in the superexcited states

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS