Formation of Negative Ions in Gases by Electron Attachment Part I. NH3, CO, NO, HCl and Cl2

Abstract

With the same method and apparatus employed in the study of negative ion formation in O2 by electron attachment, the results have been extended to all the common diatomic gases and NH3. No negative ions are formed in NH3 below an X/p of 7.5; beyond that point they are formed with increasing probability as the energy of the electrons increases. The phenomenon is interpreted as dissociation of the molecule with the formation of NH— at an electronic energy of approximately 3 volts, the NH3 molecule having itself no electron affinity. No negative ions could be formed in CO at the electronic energies available, and the molecule is presumed to have no electron affinity. Negative ions are formed by electron attachment in NO, the probability increasing with decrease in electronic energy. A linear variation in probability of attachment with pressure is also observed in NO which is due to a collision with a pair of NO molecules held together by weak attractive forces. Negative ions are formed in HCl with a probability which increases with increasing electronic energy suggesting that dissociation of the molecule occurs here as well. Similar results are obtained in Cl2 where it has been known that the energy of the attachment process must be more than sufficient to dissociate the molecule. The experiments indicate several types of attachment processes which can occur in gases and the possibilities of energy dissipation in ion formation. In general the most favored process is the carrying off of the energy by a third body involved in the process.