Three-fragment dissociation dynamics of ${\mathrm{C}}_2{\mathrm{H}}_2{}^{2+}$ dications and ${\mathrm{C}}_2{\mathrm{H}}_2{}^{3+}$ trications induced by electron capture of slow (3-keV/u) ${\mathrm{Ar}}^{8+}$ ions are investigated. Using cold target recoil ion momentum spectroscopy, the complete kinematic information and thus kinetic energy releases are determined for the three-fragment channels, ${\mathrm{C}}_2{\mathrm{H}}_2{}^{2+}\to {\mathrm{H}}^{+}+{\mathrm{C}}_2{}^{+}+\mathrm{H}$ and ${\mathrm{C}}_2{\mathrm{H}}_2{}^{3+}\to {\mathrm{H}}^{+}+{\mathrm{C}}_2{}^{+}+{\mathrm{H}}^{+}$. Then by analyzing the complete kinematics with a Dalitz plot and Newton diagram, different fragmentations, i.e., concerted or sequential pathway, are identified. For dications, the sequential fragmentation ${\mathrm{C}}_2{\mathrm{H}}_2{}^{2+}\to {\mathrm{H}}^{+}+{\mathrm{C}}_2{\mathrm{H}}^{+}\to {\mathrm{H}}^{+}+{\mathrm{C}}_2{}^{+}+\mathrm{H}$ is dominant. However, the trications mainly dissociate via the synchronous concerted fragmentation. The sequential pathway ${\mathrm{C}}_2{\mathrm{H}}_2{}^{3+}\to {\mathrm{H}}^{+}+{\mathrm{C}}_2{\mathrm{H}}^{2+}\to {\mathrm{H}}^{+}+{\mathrm{C}}_2{}^{+}+{\mathrm{H}}^{+}$, which was found to be significant at higher collision velocities, is not observed here. This distinction reveals the important role of projectile velocity on the fragmentation dynamics for some specific channels.

• Received 20 December 2018
• Revised 22 March 2019

DOI:https://doi.org/10.1103/PhysRevA.100.022705