The three-body fragmentation channel ${\mathrm{H}}^{+}+{\mathrm{H}}^{+}+{\mathrm{C}}_3{\mathrm{H}}_2{}^{+}$ of the allene trication produced by 30-keV/u ${\mathrm{He}}^{2+}$ ion impact is investigated using cold-target recoil-ion momentum spectroscopy. The two protons with different kinetic energies are found emitted sequentially from the parent trication. The presence of such a sequential deprotonation process and the absence of corresponding concerted deprotonation may result from a major molecular deformation process, e.g., ultrafast hydrogen migration, which occurs in the parent ion prior to fragmentation, and finally leads to the formation of two different protons.

• Received 22 November 2021
• Revised 26 January 2022
• Accepted 10 February 2022

DOI:https://doi.org/10.1103/PhysRevA.105.022818