The question of the relative importance of compound state (i.e., activated complex) and direct reaction mechanisms has been of central importance for the dynamical foundations of chemical kinetics [1,2]. The studies here reported indicate that in the quantum dynamics of the historically important H + H2 exchange reaction not only do both such mechanisms contribute but also that their interference plays a central role in determining the pronounced quantum oscillations of the reaction probability as a function of energy [3]. This accounts not only for the absence of such oscillations in quasiclassical calculations [4], but also for the inability of the present semiclassical formalism [5] to produce them [6]
