Two-body fragmentation dynamics of C2H22+ by electron impact: Disentangling vinylidene decarbonation from symmetric breakup

Abstract

We report experimental investigations of two-body fragmentation of ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{2+}$ induced by 1 keV electron collision utilizing an ion momentum imaging spectrometer. With the ion-ion coincidence measurement, dissociation channels ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{2+}\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{\mathrm{C}}_{2}{\mathrm{H}}^{+}$ (deprotonation) and ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{2+}\ensuremath{\rightarrow}{{\mathrm{H}}_{2}}^{+}+{{\mathrm{C}}_{2}}^{+}$ (${{\mathrm{H}}_{2}}^{+}$ formation) are directly identified, while the symmetric breakup ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{2+}\ensuremath{\rightarrow}\mathrm{C}{\mathrm{H}}^{+}+\mathrm{C}{\mathrm{H}}^{+}$ channel and vinylidene decarbonation ${\mathrm{C}}_{2}{{\mathrm{H}}_{2}}^{2+}\ensuremath{\rightarrow}{\mathrm{C}}^{+}+\mathrm{C}{{\mathrm{H}}_{2}}^{+}$ channel are not well separated in the measured time-of-flight (TOF) correlation map. In this work, by taking advantage of the independence of kinetic energy release (KER) on the dissociation angle, we are able to disentangle the events from the TOF map. Consequently, KER distributions for all four fragmentation channels are deduced, and the relative branching ratios are precisely determined from the measurements. By comparing the measured KER values with the previous calculated potential energy surfaces, pathways for the fragmentation channels are assigned.