Strong similarities between small cluster anions and electrons colliding with argon

Total destruction cross sections for negative aluminum clusters Al{sup -}{sub n} with n=2-4, and total detachment cross sections of the aluminum anion Al{sup -}, incident on Ar are measured. These values, and previously measured cross sections of C{sup -}{sub n} and Si{sup -}{sub n} with n=1-4, are compared with total (elastic plus inelastic) cross sections for electron impact on the same target. Similarities between the experimental cross sections for anions and electrons, observed in the velocity range of 0.2 to 1.8 a.u., led to a model in which the overall shape of the dependence on velocity of the anionic cross sections is well described by a convolution of the anion's outermost electron momentum distribution with the free electron-impact cross sections, and their absolute values obtained by fitting a cluster-size dependent additive constant. A geometrical interpretation is then proposed.