O in a pulsed Townsend experiment *

Swarm experiments in electronegative gases such as N₂O have been extensively studied because of their importance in discharge formation and evolution in many low-temperature plasma processes. The presence of negative ions in a discharge can considerably influence its space charge distribution and temporal development due to electron detachment processes from unstable negative ions. In this context, the pulsed Townsend technique (PTT) has proven to be a successful and efficient tool to study several plasma processes, including those related to the formation of negative ions. However, due to relatively high pressures used, mass spectrometry is discarded, hence information about the species and the densities of negative ions formed in the avalanche can only be obtained from the PTT experiment from indirect means. To overcome this problem, an experimental technique based on the PTT has been developed for studying the photodetachment of negative ions in the realm of the electron avalanche. We report and discuss the photodetachment signals and properties derived therefrom at low E/N values.