The prototypical metal-metal multiple bonded molecule, Re2Cl82-, and the brominated analogues, Re2Br82- and Re2XnY8-n2- (X = Cl, Y = Br, n = 1-3) have been prepared using electrospray ionization and investigated using low-energy collision-induced dissociation in a quadrupole ion-trap. Each of the dianions studied here decays via ionic fragmentation (i.e. loss of a halide ion) upon resonance excitation in the ion-trap, and comparison of the collision energies for activated decay reveal that the Re-Cl bond is stronger than Re-Br. CASSCF(8, 8)/LANL2DZ calculations of the ionic fragmentation potential energy surfaces of Re2Cl82- and Re2Br82- are presented to support the experimental results. (c) 2009 Elsevier B.V. All rights reserved.