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Supersonic beams of semiconductor clusters with the formula Gax As were generated by laser vaporization of a disc of pure GaAs mounted on the side of a pulsed; upersonic nozzle. These cluster beams were characterized by laser photoionization with various fixed-frequency lasers followed by time-of-flight mass spectrometry. Mass analysis of the clusters with x+ y> 10 showed all clusters in the composition range from Ga+ through Ga As to As to be

. xy x y x+ y present In roughly the amount expected from a binomial distribution. In the smaller clusters strong variations were observed from this expected binomial distribution as a result of kinetic effects in the cluster formation process. Photoionization with an ArF excimer laser at very low pulse energy revealed a pronounced even/odd alternation in the photoionization cross section of the Gax Asy clusters, depending only on the total number of atoms in the cluster …