We measured kinetic energies of the fragment ions of argon dimers multiply ionized by low-energy ${\mathrm{Ar}}^{9+}$ collisions. For $({\mathrm{Ar}}_2{)}^{4+}$ dissociation, the asymmetric channel (${\mathrm{Ar}}^{3+}+{\mathrm{Ar}}^{+}$) yield is found unexpectedly higher than the symmetric channel (${\mathrm{Ar}}^{2+}+{\mathrm{Ar}}^{2+}$) yield in contrast with previous observation for covalent molecules or clusters. For the dissociation channel $({\mathrm{Ar}}_2{)}^{2+}\to {\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{+}$, two well-separated peaks were observed, clearly evidencing that the direct Coulombic dissociation and the radiative charge transfer followed by ionic dissociation alternatively occur for the dicationic dimers. The respective intensity of these two peaks provides a direct mean to unravel the respective proportion of one-site and two-site double-electron capture, which are found equal for this collision system.

• Received 28 August 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.263202