Correlation of Sodium Atom Reaction Rates with Electron Capture Cross-sections

Abstract

THE classic Polanyi flame work^1,2 explored the reactions of sodium atoms with a very wide range of halogen compounds. For some of these the rate constants were found to be extremely large (∼ 10¹⁴ c.c. mole⁻¹ sec⁻¹), corresponding to “reaction on more than every gas-kinetic collision”. This was attributed to an electron-jump mechanism, Here essentially all collision trajectories that pass within the radius r_c at which formation of the ion-pair becomes possible lead to reaction³. This radius is given by e²/r_c = I(Na) − E^ν(X − R), where I denotes the ionization potential of the alkali atom and E^ν the vertical electron affinity of the halogen molecule. Recently, several alkali atom reactions of this type (with X − R = Br₂, ICl, PBr₃, CBr₄, SnCl₄, SF₆, etc.) have been examined in molecular beam scattering experiments⁴. The form of the angular distributions of elastic and reactive scattering and other detailed dynamical properties observed in these experiments can be very plausibly interpreted in terms of the electron-jump mechanism.