Fourier transform ion cyclotron resonance mass spectrometry has been applied to the study of the energy-resolved collision-induced dissociation of di-iron carbonyl cluster cations, Fe-2(CO)(y)(+) (y = 1-9). The electron impact ionization of Fe(CO)(5) and subsequent clustering reactions were used for the precursor ion synthesis. The sequential loss of CO ligands was observed as a typical fragmentation pathway fur all Fe-2(CO)(y)(+) clusters. Threshold values for the first ligand loss from Fe-2(CO)(1-9)(+) and for the dissociation of Fe-2(+) were determined to be 1.05 +/- 0.09, 1.23 +/- 0.10, 1.29 +/-0.09, 1.25 +/- 0.09, 0.81 +/- 0.08, 1.10 +/- 0.08, 0.82 +/-0.11, 0.33 +/- 0.08, 1.08 +/- 0.11, and 2.66 +/- 0.13 eV. The sum of these 10 values is in good agreement with the literature endothermicity for the Fe-2(CO)(9)(+) --> Fe+ + Fe + 9CO reaction. Nonmonotonic variations in the sequential thresholds are discussed in terms of spin conservation.