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 (ki) is in good agreement with flame measurements and indicates that high ionization rates are theoretically possible. The very large ionization cross sections (σi∼10−12 cm2) are due to (a) ionization from excited states lying within 2 kT 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 ki is independent of the mass of A.