On chemical activation by collisions

In the case of first order unimolecular gas reactions, such as the decomposition of nitrogen pentoxide, there is a well-known, theoretical difficulty (1) in discovering any process of activation rapid enough to maintain the full Maxwell-Boltzmann quota of activated molecules and thus to assure a first order course to the reaction. This problem has recently been treated anew by Fowler and Rideal,(2) who consider, in a somewhat new light, the possibility of activation by molecular collisions.