The chemical modification of polystyrene surfaces by low-energy (10-100 eV) SF5+, C3F5+, and SO3+ ions was studied by X-ray photoelectron spectroscopy and two-laser ion trap mass spectrometry. The mechanism of fluorination was found to be dissimilar for SF5+ and C3F5+ ions in this energy range at fluences of 10(14)-10(16) ions/cm(2). SF5+ was found to induce fluorination of the polymer surface by grafting reactive F atoms upon dissociation at impact. SFn fragments were not found to be grafted or implanted into the polymer. Sulfur was detected on the polymer surface only at incident energies above 50 eV and was found to be sulfidic in nature. In contrast, C3F5+ ions induced grafting of both reactive F atoms and molecular CmFn fragments from the dissociation of the incident projectile. Larger proportions of highly fluorinated sites and thicker fluorocarbon layers were found for C3F5+ at all energies and fluences. A variety of aliphatic and aromatic fluorine bonding environments were detected on both SF5+ and C3F5+ modified polystyrene surfaces.