Abstract
Fifteen asymmetric resonant charge transfer reactions, involving the five title atomic ions A+ and the three title molecules B have been studied in the relative (center-of-mass) energy range 1–10 eV. Two different tandem mass spectrometers were used to measure limiting cross-sections at the highest energies. Time-of-flight and retarding-potential-analysis techniques were used to characterize the contribution from non-resonant processes, occurring with momentum transfer at low impact parameters.
An attempt is made to correlate the magnitudes of the cross-sections for A+ + B → products with molecular parameters of the original reactants: (i) the Franck—Condon factors for B → B+, and (ii) the cross-section for A+ + A → A + A+. The Franck—Condon factors for B → B+ are shown not to correlate quantitatively, although a propensity rule — low factors legislate low cross-sections — does apply. The dependence of the cross-section on the nature of A correlates qualitatively with the square root of the symmetric charge transfer cross-section for A+ + A → A + A+. The incorporation of all these factors, within the context of Förster theory (which treats the transfer of excitation energy
), is considered for charge transfer. Qualitative but not quantitative correlations are found, and a formal justification for this is noted. The implications of these results for the mechanism of these reactions at thermal energies are briefly considered.