To gain insight into surface processes in plasma processing, basic ion beam experiments are performed on two representative polyatomic-ion species: hydrocarbon ions CHx+for deposition processes and fluorocarbon ions CFx+for etching processes(x=1,2,…). A single ion species is extracted from an inductive plasma via a mass filter and directed onto aluminum surfaces at energies100 eV) incidence of both CHx+and CFx+species gives rise to dissociation into smaller fragment ions, probably via electronic excitation.