Abstract
An expression is derived relating state‐selected or state‐averaged molecular beam reaction cross sections of endothermic reactions to observed rate constants for the inverse (exothermic) reactions. An approximation of Anlauf, Maylotte, Polanyi, and Bernstein is used, together with bimolecular microcanonical activated complex theory [R. A. Marcus, J. Chem. Phys. 45, 2138 (1966)].