Calculation of thermal ionization rate coefficients of alkali atoms in molecular gases

The Wigner–Keck theory of dissociation and recombination is applied to the thermal ionization reaction A+N2→A++e −+N2, where A is an alkali atom. The calculated upper‐bound ionization rate coefficient (k i ) is in good agreement with flame measurements and indicates that high ionization rates are theoretically possible. The very large ionization cross sections (σ i ∼10−12 cm2) are due to (a) ionization from excited states lying within 2 k T of the ionization limit, and (b) inelastic energy transfers between electrons and the collision partner. In contradistinction to conventional collision theories, the present work shows that k i is independent of the mass of A.