The collision-induced dissociation (CID) of Cs4Imath image to form Cs3Imath image has been investigated by mass-analysed ion kinetic energy spectroscopy, When helium was used as collision gas the CID process was accompanied by sizable loss of translational energy in the collisional-activation step. However, use of krypton or xenon as collision gas yielded product ions with translational energies higher than that observed for unimolecular reaction in the absence of collision gas. Neon and argon provided intermediate behaviour. Extensive experiments designed to investigate possible explanations for these observations left superelastic collisions of an excited state as the only possibility. Since nothing is known about the structures and electronic states of species like Cs4Imath image, the necessarily speculative discussion is based upon general considerations of coupling of translational and electronic energies via crossings between states of the transitory collision complex. These observations emphasise the complexity of the possible processes which can occur as a result of collisions in the keV range.