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

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 3s5S0 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+.