Electron impact ionization of small argon clusters

The dynamics of cluster ions following electron impact ionization of Ar-n, n = 3, 4, have been modelled theoretically and the calculated fragmentation probabilities compared with recent measurements using scattering deflection techniques. The calculations have been conducted using a hybrid quantum/classical treatment on a manifold of 3n coupled potential energy surfaces of the ions determined by a diatomic-in-molecules model plus polarization terms. Branching ratios into the different fragmentation channels have been calculated. The results are in good agreement with measured ion abundances. In particular, in the calculations Ar-3(+) ions are not found to be produced by electron impact ionization of Ar-3 and Ar-4, in agreement with the experimental findings.