(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 nu(1) stretching mode (3307 cm(-1) for C2H2+, 2572 cm(-1) for C2D2+), as well as the frequencies for the bending mode: trans-nu(4) (694 cm(-1) for C2H2+, 586 cm(-1) for C2D2+) and cis-nu(5) (775 cm(-1) for C2H2+, 569 cm(-1) for C2D2+) of the cations. (C) 2003 American Institute of Physics.