Reactive scattering of alkali dimers: chemi-ionization

Abstract

Measurements of total cross sections Q_i for chemi-ionization in scattering of a K₂ dimer beam by a range of halogen containing molecules, at translational energies E ∼ 7–11 kcal mol^-1, are reported. Substantial cross sections, Q_i ∼ 2–10 Ų are exhibited by the halogen molecules Br₂, ICl, IBr, I₂. Distinctly lower values Q_i ∼ 0·1–0.2 Ų are exhibited by BrCN and the mercuric and stannic halides, HgX₂, SnX₄. The results show a close correlation with the chemi-ionization exoergicities, particularly for formation of a K⁺,X^- ion pair. These chemi-ionization data and results from previous reactive scattering studies are compared, in order to estimate relative reaction yields for different reaction paths. The reaction dynamics for K₂ with halogen molecules and cyanohalides are rationalized in terms of the electronic structure of the potential surface, where the orientation of the K₂ dimer plays a crucial role.