The kinetic energies of Ir-m(CO)(n)(+) ions observed in the high resolution TOF-SIMS of Ir-4(CO)(12) layer have been estimated using the post-acceleration electrode method. The observed kinetic energy of secondary ion depends on the number of coordinated CO molecules, but not on the cluster size of Ir-m(+) shell. The signal of Ir-5(CO)(12)(+) ion is missing in the observed mass spectrum. The analysis of the uni-molecular dissociation reactions of the complex ions and DFT calculations have shown that this is due to the structural change of Ir-5(+) shell with the increase of the coordinated CO molecules. (C) 2012 Elsevier B. V. All rights reserved.