Activated Complexes of Fast Bimolecular Reactions

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Abstract
The specific rates of radical association and ion‐molecule reactions (e.g., CH3+CH3→C2H6, H2++H2→H3++H, etc.) were calculated with the use of the absolute reaction‐rate theory and were compared with the observed values. Except for some special reactions, the observed rates agree with the theoretical values with a transmission coefficient, 1 to 1/10. The over‐all entropy change of the backward reactions ΔSb were calculated by the usual statistical thermodynamical method, and also the activation entropy of the backward reactions, ΔSb‡, were calculated. The two quantities agree fairly well. From these results it was concluded that the activated complexes of the fast reactions have loose structures such that the reactant molecules (radicals or ions) rotate freely with the restriction that they cannot move independently in the translational degrees of freedom.