Secondary-ion yields from surfaces bombarded with keV molecular and cluster ions

We have measured negative secondary-ion yields from phenylalanine, CsI, and Au bombarded by complex ions of 5--28 keV. The primary ions were organic monomer and dimer ions and clusters of CsI. Large enhancements occur in the measured secondary-ion yields for more complex projectiles. We show that secondary-ion yields of Au^- atomic species are related to the square of the projectile momentum.