The formation of carbonaceous clusters in ion-irradiated polymer films was investigated extensively. Information about these clusters may be obtained with ultra violet-visible (W-vis) spectroscopy. The optical band gap (E-g), calculated from the absorption edge of the UV spectra of these polymers, can be correlated to the number of carbon atoms (N) in a cluster with the modified Tauc equation. The structure of the cluster is also related to E-g; for example, a six-membered-benzene-ring-type structure has an E-g of approximate to 55.3 eV, whereas a buckminsterfullerene-type structure has an E-g of approximate to 4.9 eV. These clusters are responsible for the electrical conductivity in these films. In this work, polycarbonate films (20 mu m thick) were irradiated with 45-MeV Li ions at fluences of 1 x 10(12) to 1 x 10(13) cm(-2) and were characterized with UV-vis spectroscopy and impedance measurements. The E-g values, calculated from the absorption edge in the 280-315-nm region with the Tauc relation, varied from 4.39 to 4.35 eV for the pristine and various irradiated samples, respectively. The cluster size showed a range of 60-62 carbon atoms per cluster. The sheet conductivity (sigma(dc)) and loss (tan delta) values of 10(-16) Omega(-1)cm(-1) and 10(-3) for the pristine sample changed to 10(-15) Omega(-1)cm(-1) and 10(-2), respectively, for the irradiated samples. This increase in the values of sigma(dc) and tan delta may be correlated to the increase in the size of the carbonaceous clusters. This study provides insight into the mechanism of electrical conductivity in irradiated polymers.