Electron-impact-like feature in triple fragmentation of CO23+ under slow proton impact

Abstract

We have studied the three-body breakup of ${\mathrm{CO}}_{2}^{3+}$ created by the impact of slow ($v<1$ a.u.) protons on ${\mathrm{CO}}_{2}$. Employing the coincidence momentum imaging technique, we have obtained the correlated momenta of the three fragments, ${\mathrm{O}}^{+}+{\mathrm{C}}^{+}+{\mathrm{O}}^{+}$, and thence the kinetic energy release (KER) distribution. By examining the Dalitz plots for the three-body breakup, we separate the sequential and concerted breakup events and analyze the corresponding KER distributions. Based on the potential energy curves reported in the literature, we identify the possible transient states of ${\mathrm{CO}}_{2}^{3+}$ that lead to the different features in the KER distribution. We find that under ${\mathrm{H}}^{+}$ impact, the KER distribution shows a low-energy feature, which is seen in the case of electron impact, but not under the impact of slow or fast highly charged ions. This feature is identified as arising via the low-lying ${}^{2}\mathrm{\ensuremath{\Pi}}$ and ${}^{4}\mathrm{\ensuremath{\Pi}}$ states of the transient molecular ion. We further note that slow protons, which are the simplest of projectiles, are able to excite the ${\mathrm{CO}}_{2}$ molecule to a broad range of triply ionized transient states, spanning those accessed by the impact of slow highly charged ions and also those accessed by electron impact, but with varying probabilities.