Three-body fragmentation of methane dications produced by slow Ar8+ -ion impact

Abstract

The three-body fragmentation dynamics of ${{\mathrm{CH}}_{4}}^{2+}$ dications induced by single-electron capture of slow (3-keV/u) $\mathrm{A}{\mathrm{r}}^{8+}$ ions is investigated. The experiment is performed on a newly built, highly charged ion collision platform which consists of an electron cyclotron resonance ion source and a cold target recoil ion momentum spectroscopy (COLTRIMS) setup. Using the COLTRIMS methodology, the complete kinematical information is determined for two three-body breakup channels, ${{\mathrm{CH}}_{4}}^{2+}\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{{\mathrm{CH}}_{2}}^{+}+\mathrm{H}$ and ${{\mathrm{CH}}_{4}}^{2+}\ensuremath{\rightarrow}{{\mathrm{H}}_{2}}^{+}+\mathrm{C}{\mathrm{H}}^{+}+\mathrm{H}$. Then analyzing the complete kinematics with the Dalitz plot, very different fragmentation mechanisms (e.g., sequential and/or concerted pathway) are clearly identified for the two channels. To confirm the existence of some possible fragmentation pathways, we also simulate corresponding Dalitz plots employing a simple classical mechanical model. For the ${\mathrm{H}}^{+}+{{\mathrm{CH}}_{2}}^{+}+\mathrm{H}$ channel, the dependence of the fragmentation pathway on its kinetic energy release is studied, which reflects the different nature of the corresponding states of ${{\mathrm{CH}}_{4}}^{2+}$ dications. Furthermore, the kinetic energy ratio of two ionic fragments is analyzed to infer the three-body fragmentation mechanism of ${{\mathrm{CH}}_{4}}^{2+}$ dications.