[en] Rate constants and activation energies for selected initial rotational levels, thermally averaged over vibrational states and translational energies, are calculated for Ar+H₂→Ar+H+H by the Monte Carlo quasiclassical trajectory method. The results show that activation energies for high rotational quantum numbers exceed those estimated from centrifugal barrier heights. To characterize the rotational-level model of diatomic dissociation, we tabulate rate constants, activation energies, and other properties of dissociative collisions as functions of initial rotational quantum number j for conditions of thermal vibrational and translational degrees of freedom at 4500 K. Under equilibrium conditions, dissociation from a given j level is shown to occur primarily from the topmost v state of that j level