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Indium-sodium (In,Na,) bimetallic clusters were produced by two independent laser vaporization methods.Ionization potentials (IPS) of the In,Nam clusters were measured up to m = 2 using a tunable ultraviolet laser combined with a time-of-flight (TOF) mass spectrometer. At small sizes (n = 3-1 5 ) , the ionization potentials decrease by 0.1-0.8 eV with the addition of N a atom@), whereas the IPS of larger In, (15 I n I 27) clusters do not decrease with N a addition. Moreover, IPS of In7Nal and In13Nal clusters are higher than those of In7 and Inl3, and the IP increments can be explained by electronic shell closings of the l p (8e) and 2p shell (40 e), where In atoms in the clusters are monovalent and trivalent, respectively. The electronic shell structure was also examined by a magic number in mass distributions of In,Na,-cluster anions; the In12Na3-cluster can be observed as magic numbers, corresponding to the 2p shell closing. In contrast, no electronic shell structure is observed in pure In, clusters around n = 13. These results indicate that Na atom addition can induce s / p hybridization in the In, clusters. W e also present mass distributions of aluminum-sodium cluster anions, Al,Na,-, whose feature can be understood by the electronic shell model.

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