C K-edge X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (PES) measurements were taken for hydrogenated amorphous carbon films before and after ion beam irradiation. The C K-edge XANES and valence-band PES spectra indicate that irradiation breaks C-C bonds to form C=C bonds and has a similar effect on the electronic structures of the films, irrespective of the hydrogen content. The valence-band PES measurements reveal that ion beam irradiation markedly enhances the density of carbon pi states in the vicinity of the Fermi level. (c) 2007 Elsevier B.V. All rights reserved.