Exothermic Ion—Molecule Reactions

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Abstract
Dissociative charge‐transfer reactions between rare‐gas He+, Ne+ ions and diatomic N2, O2, CO, NO molecules have been studied as a function of reactant‐ion velocity. N+, O+, and C+ fragment ions are the major reaction products observed in these exothermic reactions. Experimental cross sections and corresponding rate constants for thermal‐energy ions are in semiquantitative agreement with the theoretical rates calculated from the long‐range ion—induced‐dipole potential. A reversed‐repeller technique was used to probe the kinetic‐energy distributions of the ionic reaction products and the experimental (0.2 to 1 eV) distributions so obtained are well correlated with the heats of the respective reactions. The kinetic energies of the product N+ and O+ ions were shifted to lower values when 3He+ was substituted for 4He+ ions in the NO and O2 reactions. This shift in product‐ion kinetic energy rules out accidentally resonant charge‐transfer processes involving excited product atoms and is consistent with a two‐body breakup mechanism of transitory HeN+ and HeO+ at low reactant‐ion velocities.

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