Electron bombardment fragmentation of Ar van der Waals clusters by scattering analysis

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Abstract
Arn clusters generated in a supersonic nozzle beam are investigated by exploiting their different kinematical behavior in a scattering experiment. In a crossed molecular beam experiment the Arn clusters are scattered from He atoms at E=69.7 meV. By measuring the angular and velocity distributions of the scattered clusters, the different species can be separated from each other. In this way fragmentation probabilities of small Arn clusters up to n=6 by electron impact ionization are measured. The influence of collisional dissociation of the dimer is accounted for by classical trajectory calculations. The dimer fragmentation is found to be f21=0.40±0.05, while the trimer totally fragments to dimers ( f32=0.7±0.3) and monomers ( f31=0.3). All clusters with n from 4 to 6 appear with a probability of 0.95 on the dimer ion mass.