The relative intensity distribution of the [Rb,K14-nI13](+) mixed nanocrystals containing a "magic" number of 14 metal cations and 13 iodide anions is examined. These nanocrystals were generated through sputtering of mixed RbI/KI solids using fast atom bombardment and analyzed by use of a double-focusing sector-field mass spectrometer. The relative intensities of the observed peaks are found to have a "bimodal" distribution with a maximum near n = 7. This observation is explained by assuming : (a) a rate of formation that is proportional to the number of isomers that can be formed for each mixed nanocrystal, and (b) a rate of dissociation that is insensitive to the composition of the mixed nanocrystal. The later assumption leads to the conclusion that the internal energies of these mixed nanocrystals are similar and independent of their composition. This conclusion is supported by the results of Monte Carlo simulation annealing as well as by the similarity of the known lattice energies of KI and RbI bulk crystals.