Electron attachment and detachment in pure O 2 and in O 2-CO 2 and O 2-H 2O mixtures

Abstract

Electron attachment and detachment processes of possible interest in combustion problems are radiative attachment and photodetachment, dissociative attachment and associative detachment, and three-body attachment and collisional detachment. These processes are reviewed briefly and typical rate coefficients are given. Measurements have been made of the rates of three-body electron attachment and collisional detachment in pure O 2 and in O 2 −CO 2 and O 2 −H 2 O mixtures. Extrapolation of these results to thermal energies at temperatures from 375° to 583°K, yields rate coefficients and equilibrium constants for the electrons and negative ions. Ion identification is based on the density dependence of the equilibrium data. The attachment and detachment coefficients and the equilibrium constants obtained for pure O 2 are consistent with the assumption that the process being studied is e +2O 2 O 2 − +O 2 and that the electron affinity of the O 2 − molecule is 0.44 eV. The rate coefficient and equilibrium constant data for the O 2 −CO 2 mixtures are consistent with the reaction e +O 2 +CO 2 CO 4 − with an electron affinity of 1.2 eV but with a very high degree of freedom of internal motion. Measurements in O 2 −H 2 O mixtures show: that the rate of negative ion formation by thermal electrons in pure H 2 O is negligibly small; that the three-body attachment coefficient for negative ion formation due to collisions between electrons, oxygen molecules, and water molecules is about four times that for electrons and two oxygen molecules; and that ions of very high stability are formed at a rather slow rate compared to that observed in O 2 −CO 2 mixtures.