Laser ablation of YBa2Cu3O7-δ (YBCO) superconductor samples was investigated in a Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) to determine the morphology of the cluster ions produced. Cluster ion series increase exclusively by addition of BaO and Y2O3 neutral species. Collisionally induced dissociation (CID) of the clusters indicated that BaO was coordinated to the yttrium atoms, leading to preferential loss of BaO, but was coordinated to other BaO units in copper clusters, where Cu loss was observed. The degree of clustering and ion distributions were dependent on laser fluence but were independent of the Nd:YAG laser wavelength. The results suggest that gas-phase growth processes are responsible for the cluster formation. The heats of formation for the cluster ions become more negative as cluster ions size increases. © 1992 American Chemical Society.