Bonding character of bimetallic clusters AunXm (X = Al, In, Cs)

Bimetallic cluster ions of composition AunXm+ (X = Al, In, Cs) have been studied using time-of-flight mass spectrometry. The mass spectra of gold-aluminum clusters exhibit electronic shell effects for arbitrary composition. Differences in the sequence of shell closings for gold-rich and aluminum-rich clusters can be explained in terms of the differing free electron densities of the two materials. Spectra of gold-indium clusters indicate the formation of electronic shells only for gold-rich species. Among clusters with a higher indium content, the series In+(InAu)(n) is found to have enhanced stability. This indicates an appreciable charge transfer from gold to indium atoms. Similar spectra are found for the system gold-cesium, where Cs+(CsAu)(n) are most stable. (C) 1999 American Institute of Physics. [S0021-9606(99)02320-X].