The collisional deactivation of HgBr(B-2 Sigma) by Ar has been studied using quasiclassical trajectories calculations. The results, which present an average strong collision behavior, are described by a double-exponential energy-transfer function and show the occurrence of supercollisions, in analogy to other (weak collisions) studies. The transference of large amounts of energy occurs when the Ar atom situates near the internuclear axis of HgBr, when the bond is at maximum elongation, and receives the impact of bromine during the closing phase of the vibration. This process is facilitated by the anharmonic motion of HgBr.