The role of high Rydberg states in enhanced O^- formation in a pulsed O₂ discharge

Formation of O^- ions in a pulsed discharge of O₂ was investigated in a Langmuir-probe-assisted photodetachment experiment. A large enhancement of negative ion formation was observed in the afterglow. Experimental results are consistent with O^- formation via electron attachment to high Rydberg states of O₂ that survive into the afterglow. Such excited states can be produced by high-energy electron impact during the discharge. The lifetime of high-Rydberg molecules is estimated to be longer than 10 microseconds. The efficient production of O^- ion by electron attachment to high-Rydberg O₂ molecules was further confirmed in a laser excitation experiment. The O^- ions and O atoms produced via enhanced dissociative electron attachment to excited states of O₂ may be important for the chemical processes that occur in pulsed plasma remediation of contaminated air.