Fragmentation dynamics of acetylene in collision with highly charged ions: Concerted and sequential breakage of CH and CC bonds

The three-body fragmentation of C₂H₂³⁺ to H⁺ + C⁺ + CH⁺ as a consequence of one CH and one CC bond breaking is investigated by 50-keV/u Ne⁸⁺ impact. All three fragments are detected in coincidence with a scattered projectile (either Ne⁷⁺ or Ne⁶⁺) employing a reaction microscope, and their momentum vectors as well as the kinetic energies were obtained. Four distinguished structures are observed in the energy correlation spectra, indicating that abundant fragmentation mechanisms contribute to the H⁺ + C⁺ + CH⁺ channel. The Newton diagrams and Dalitz plots are employed to trace fragmentation mechanisms. We found that both the concerted fragmentation and the sequential pathway with CH bond breaking prior to CC contribute to this channel. The possible electronic states of the C₂H₂³⁺ precursor that may contribute to the identified fragmentation mechanisms are analyzed with the help of quantum chemical calculations. Furthermore, the influence of the collision dynamics between the projectile and the target to the dissociation mechanisms is discussed by comparing the contributions from the reaction channel with transferring one electron while ionizing the other two, i.e., T1I2, and the reversed channel T2I1. The T2I1 channel is observed to be more efficient to initiate fragmentation mechanisms leading to higher kinetic-energy release.