Ionizing Collision Reactions of Electronically Excited Atoms and Molecules

Abstract

Ionization reactions that result from thermal collisions of electronically excited atoms or molecules are often termed chemiionization reactions. There is, however, no general agreement on a definition of the limits of the term chemiionization in the sense that we can say this or that reaction is or is not a chemiionization process. Thus Berry,(1) in a recent review, includes in the term “all the processes that result in the formation of free charges, electrons or ions, under the conditions of chemical reactions.” This rather broad definition includes all the ionization processes possible in collisions involving electronically excited species and, in addition, includes autoionization and very high-temperature collisions of species in their ground electronic states. Fontijn,(2) on the other hand, defines chemiionization as “a process by which the number of elementary charge carriers is increased as a direct result of the formation of new chemical bonds.” This more limited definition excludes a number of ionization possibilities in thermal collisions involving electronically excited entities, as well as autoionization processes; it would include high-temperature ionizing collisions of species in ground electronic states.