Molecular-dynamics simulation is presented for an argon cluster, Ar-2057, excited impulsively via instantaneous kinetic-energy deposition to constituent atoms in a hemispherical region. A critical energy is found for the fragmentation process of an unexcited volume of the cluster, above which fission is induced, whereas ejection of atoms predominates below this threshold energy. The fission process is shown to be accompanied by a shock wave propagating across the cluster. This simulation provides a qualitative model for the disintegration dynamics of a liquid micro-droplet excited by a mid-infrared laser pulse tuned to strong absorption [A. Terasaki, J. Phys. Chem. A 111 (2007) 7671]. (C) 2009 Elsevier B. V. All rights reserved.