Ultrahigh-mass cluster ions ($\frac{m}{z}>18\mathrm{}000$) of the type ${\left[M{\mathrm{}\left(\mathrm{MX}\right)\mathrm{}}_n\right]}^{+}$ have been produced by xenon-ion bombardment of CsI and detected by a high-performance secondary-ion mass spectrometer. The mass spectra (ion intensity versus $n$) show anomalous behavior which is correlated with hypothesized dominance of cubiclike clusters having low surface energies.

• Received 22 June 1981

DOI:https://doi.org/10.1103/PhysRevLett.47.1046