Dissociation by Electron Impact of Oxygen into Metastable Quintet and Long-Lived High-Rydberg Atoms

Abstract

Excitation of O₂ by low energy electrons leads to its dissociation with the formation of metastable oxygen atoms. The metastable atoms which have been detected are in the ${\text{3s}}^5{S}^0$ state at 9.14 eV and in long‐lived high‐Rydberg states. A molecular beam time‐of‐flight method is used to measure their translational energy. Electron impact excitation functions are given for the formation of metastable atoms. High‐Rydberg atoms result from dissociation of initially formed high‐Rydberg molecules. Because a high‐Rydberg molecular orbital is nonbonding, dissociation is determined by states of the core O₂⁺ ion. This mechanism is supported by general agreement between the observed kinetic energy distribution of high‐Rydberg atoms and the kinetic energy distribution of O⁺ from dissociative ionization of O₂. The fragment kinetic energy distributions are discussed in terms of known and predicted states of O₂ and O₂⁺.