The C K-shell photoelectron mainline of C 2H 2 molecules have been measured at photon energies 295–350 eV. The gerade and ungerade symmetries of the core-ionized states, 1 σ g and 1 σ u, are resolved. Resonance enhancement is found only in the 1 σ g photoionization cross-section and assigned to the σ 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 σ u photoionization channel, suggesting that the channel coupling is negligible.