Interatomic Coulombic Decay as a New Source of Low Energy Electrons in Slow Ion-Dimer Collisions

We provide the experimental evidence that the single electron capture process in slow collisions between ${\mathrm{O}}^{3+}$ ions and neon dimer targets leads to an unexpected production of low-energy electrons. This production results from the interatomic Coulombic decay process, subsequent to inner-shell single electron capture from one site of the neon dimer. Although pure one-electron capture from the inner shell is expected to be negligible in the low collision energy regime investigated here, the electron production due to this process overtakes by 1 order of magnitude the emission of Auger electrons by the scattered projectiles after double-electron capture. This feature is specific to low charge states of the projectile: similar studies with ${\mathrm{Xe}}^{20+}$ and ${\mathrm{Ar}}^{9+}$ projectiles show no evidence of inner-shell single-electron capture. The dependence of the process on the projectile charge state is interpreted using simple calculations based on the classical over the barrier model.

Figure 1

Illustration of the CE, RCT, and ICD processes in collisions between multicharged ions and neon dimers. The potential energy curves were adapted from [19, 20]. The KER distribution expected for each process is schematized on the right.

Figure 2

KER distributions obtained for the ${\mathrm{Ne}}^{+}(2p^{-1})+{\mathrm{Ne}}^{+}(2p^{-1})$ fragmentation channel with ${\mathrm{O}}^{3+}$, ${\mathrm{Ar}}^{9+}$, and ${\mathrm{Xe}}^{20+}$ projectiles. Events associated to TDC and SCC are displayed on the left and right panels, respectively. The dashed lines correspond to the fitted distributions for the CE and RCT processes and the solid lines to their sum. The red line displayed in the layer (f) shows the ICD distribution extracted from [3]. For each process, the peak position is indicated by vertical lines.

Figure 3

Experimental and calculated relative yields of the CE, RCT, and ICD processes contributing to the ${\mathrm{Ne}}^{+}(2p^{-1})+{\mathrm{Ne}}^{+}(2p^{-1})$ fragmentation channel. Both TDC and SCC processes are taken into account. Experimental uncertainties, not indicated here, were estimated to be about 0.05.