Intra-molecular H2+ formation in the core-excited HCCH probed by multiple-ion coincidence momentum imaging

In the HCCH molecule, H2+ ions have been produced only at the 1s→π* excitation, suggesting that the H2+ ion formation is mediated by the core excitation. The nuclear motion in the C 1s−1π* core-excited state is probed using a multiple-ion-coincidence imaging technique and the enhanced cis bending motion is found by examining the H–H correlation angle distributions. The H2+ formation is thus attributed to the cis bending motion caused in the C 1s−1π* state.