Electron-impact fragmentation ofCl2−

Abstract

A merged beam technique has been used to investigate the fragmentation of the ${\mathrm{Cl}}_{2}^{\ensuremath{-}}$ ion in collisions with electrons over an energy range of $0--200\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. We have measured absolute cross sections for detachment, detachment plus dissociation and dissociation processes. Over the energy range studied, the dominant breakup mechanism is dissociation. Dissociation is relatively enhanced in the ${e}^{\ensuremath{-}}+{\mathrm{Cl}}_{2}^{\ensuremath{-}}$ collision system due to the suppression of the normally dominant detachment process, as a result of the large difference between the equilibrium internuclear distances of the ${\mathrm{Cl}}_{2}$ and ${\mathrm{Cl}}_{2}^{\ensuremath{-}}$ ground state potential curves. A prominent structure is observed just above the threshold in the ${\mathrm{Cl}}^{\ensuremath{-}}+\mathrm{Cl}+{e}^{\ensuremath{-}}$ dissociation channel. It is proposed that the structure is a resonance associated with production and rapid decay of an excited state of the doubly charged ${\mathrm{Cl}}_{2}^{\ensuremath{-}}$ ion. A plausible mechanism for production of the di-anionic state based on an excitation plus capture process is suggested.