Figure 1

Sketch of the important energy levels in Ne and ${\mathrm{N}\mathrm{e}}_2$. In Ne, a $2s$ vacancy cannot decay by an Auger process, because the transition from ${\mathrm{N}\mathrm{e}}^{+}$ $2s^{1}2p^6$ to the final state ${\mathrm{N}\mathrm{e}}^{2+}$ $2s^{2}2p^4$ by electron emission would consume energy (left panel). For a Ne cluster the situation is different. In this case a $2s$ vacancy can relax from ${\mathrm{N}\mathrm{e}}^{+}$ $2s^{1}2p^6$ to $(\mathrm{N}{\mathrm{e}}^{\mathrm{+}}2s^{2}2p^5{)}_2$ by ICD. So, in the final state the two ${\mathrm{N}\mathrm{e}}^{+}$ $2s^{2}2p^5$ sites in the cluster will have a significantly lower Coulomb repulsion than ${\mathrm{N}\mathrm{e}}^{2+}$. Subsequently, the cluster will fragment by Coulomb explosion. The ionization potential (IP) and the double ionization potential (DIP) are given in the figure.Reuse & Permissions

Figure 2

Photon excited electron spectra of Ne clusters with an average size of $⟨N⟩=70$ atoms. The spectra depicted by thick solid lines are taken at different photon energies above the Ne $2s$ threshold. For comparison, in every panel a spectrum recorded below the $2s$ threshold is shown (shaded region). At 51.5 and 63 eV, we also show the spectrum obtained with a Ne beam at temperatures slightly higher than the onset of condensation (thin, dotted lines). All spectra were measured as one series and have been normalized by the photocurrent of the last refocusing mirror of the beam line. The signal at kinetic energies below 0.4 eV (left of vertical, dashed line) contains contributions of unphysical, scattered electrons.Reuse & Permissions

Figure 3

Low kinetic energy electron spectra of Ne (solid line) and Ar (shaded region) clusters, normalized as in Fig. 2.Reuse & Permissions