A mass spectrometric investigation of the photofragmentation behavior of mixed clusters composed of C-70 molecules and iridium atoms (C-70)(m)Ir-x (m=2, 3; x >2) reveals that coalesced fullerenes C138-2n and C206-2n (n=0, 1, 2,...) are the predominant reaction products at high laser intensities. More detailed tandem time-of-flight experiments on mass selected (C-70)(2)Ir-x indicate that the efficiency of the coalescence reaction increases with increasing iridium content in the precursor cluster. Most probably the formation of strongly bound IrC molecules plays an important role for the reaction mechanism. For comparison, the fragmentation behavior of preselected (C-70)(2)Co-5 is also investigated. (C) 2001 American Institute of Physics.