Polycarbonate films were irradiated by MeV ions, including carbon clusters C-n(+) (n = 1-5) with the same atomic dose and energy, Cl+, Ti+, and Ni+. UV-VIS-NIR spectrophotometer was employed to detect the optical absorption of irradiated samples. From the absorption spectrum, it is found that the damage cross-section of samples irradiated by carbon clusters increases non-linearly with the increase in cluster size. It should be induced by the collective effect and the non-linear effect of cluster ions. Attenuated total reflectance was employed to analyze the change of chemical bonds on the surface of samples. Some new bonds such as -OH are formed. (c) 2006 Elsevier B.V. All rights reserved.