Transient nonequilibrium effects in the attachment of electrons to chlorofluoroethanes

摘要

A study of the transient behavior of a nonequilibrium electron swarm in argon together with a small amount of an electron attaching chlorofluoroethane is carried out. The initial electron distribution function is assumed to be a delta function in energy and the subsequent temporal evolution of the distribution function is determined with the twohyphen;term solution of the Boltzmann equation. Owing to the small electron mass relative to the other constituents, the Boltzmann equation reduces to a Fokkerndash;Planck equation. Quite generally, the electron attachment process affects the nature of the electron thermalization and vice versa, that is, thermalization and reaction are coupled processes. The experimental determination of attachment rate coefficients involves the assumption that the attachment process has an insignificant effect on the electron distribution function and that the thermalization to a steady state occurs sufficiently quickly so that the attachment kinetics can be described by the steady state electron distribution. In the present paper, the coupling of the thermalization process and the attachment reaction is studied in detail. The time dependence of the electron energy and the attachment rate coefficient are considered for several chloroflouroethanes which exhibit either attachment cooling or attachment heating. A discussion of these steady state effects is presented in connection with similar concepts in hot atom chemistry.