Theory of near-threshold endoergic associative ionization reactions of atoms

A multichannel quantum defect (MQD) method incorporating the configurational interaction of Rydberg and valence dissociative states is used to develop a quantum approach to the theory of endoergic associative ionization reactions of atoms. It is shown that near the ionization threshold the total cross section σ of the associative ionization reaction goes as the energy E reckoned from the threshold of the reaction, i.e., σ ∼ E. The influence of quasidiscrete states of valence configurations (which are populated in atomic collisions) on the ionization spectrum is investigated. Various limiting cases are considered. As a concrete example the associative ionization cross section is calculated for the reaction N + O → NO+ + e-, and the result is found to agree satisfactorily with an existing experiment. The temperature dependence of the associative ionization rate constant for this process is obtained over a wide range of temperature