We investigate the fragmentation dynamics of the diiodoacetylene (${\mathrm{C}}_2{\mathrm{I}}_2$) molecule under the impact of 10-keV/u ${\mathrm{Ar}}^{8+}$ ions, focusing on complete three-body ionic breakup channels. The experimental results, analyzed using Newton and Dalitz plots, are compared with classical trajectory simulations based on a pure Coulomb-repulsion model. We identify the presence of concerted and sequential fragmentation mechanisms of ${\mathrm{C}}_2{\mathrm{I}}_2{}^{3+}$. Concerted breakup is found to be the dominant pathway across all channels, where near-perpendicular emission of the lightest fragment is observed relative to its heavier counterparts. Sequential fragmentation proceeds predominantly via the intermediate ${\mathrm{C}}_2{\mathrm{I}}^{2+}$, which dissociates into either ${\mathrm{C}}_2{}^{+}+{\mathrm{I}}^{+}$ or ${\mathrm{C}}^{+}+{\mathrm{CI}}^{+}$ fragments. An alternative sequential route through ${\mathrm{CI}}^{2+}$ leading to ${\mathrm{C}}^{+}+{\mathrm{I}}^{+}$ is also possible. These sequential pathways reveal clear signatures of intramolecular scattering, which are governed by the lifetime of the intermediate dication. Our analysis shows that the internal energy of ${\mathrm{C}}_2{\mathrm{I}}_2{}^{3+}$ plays a critical role in determining the preferred dissociation pathways.

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• Molecular dissociation