The C K-shell photoelectron mainline of C2H2 molecules have been measured at photon energies 295-350 eV. The gerade and ungerade symmetries of the core-ionized states, 1 sigma(g) and 1 sigma(u), are resolved. Resonance enhancement is found only in the log photoionization cross-section and assigned to the sigma(u)(*) shape resonance. The photoelectron asymmetry parameter takes a minimum value at the shape resonance energy. The shape resonance energy decreases with increase in the vibrational quantum number. No correlational shape resonance appears in the 1 sigma(u) photoionization channel, suggesting that the channel coupling is negligible. (c) 2006 Elsevier B.V. All rights reserved.