(3 + 1)-resonance enhanced multiphoton ionization-photoelectron spectroscopy (REMPI-PES) has been carried out via various low vibrational levels of the D, F, and E states belonging to the (3d-4s) supercomplex of acetylene. The photoelectron analysis takes into account the Renner-Teller coupling occurring in the ion ground state. In the 74 500-76 500 cm-1 energy range, the coupling between the F Rydberg state and E valence state is strongly revealed through the photoelectron spectra. Moreover, the vibrational analysis of the REMPI-PES spectra enlighten the controversial geometry of the E valence state. They strongly indicate a planar trans-bent geometry of the E valence state, quantitatively confirmed by an ab initio study. This study confirms the tentative frequencies for the nu1 stretching mode (3307 cm-1 for C2H₂⁺, 2572 cm-1 for C2D₂⁺), as well as the frequencies for the bending mode: trans-nu4 (694 cm-1 for C2H₂⁺, 586 cm-1 for C2D₂⁺) and cis-nu5 (775 cm-1 for C2H₂⁺, 569 cm-1 for C2D₂⁺) of the cations.