$2p$ correlation satellites in neon clusters investigated by photoemission

Photoelectron spectra of the $2p$ correlation satellites in free Ne clusters have been measured for a number of cluster sizes. With the exception of the least strongly bound prominent satellite line, derived from the $2p^4\left({}^{1}D\right)3s$ atomic configuration, the satellites in the cluster show a broadening with the increase of cluster size, but no pronounced energy shift with respect to the atomic lines. The $2p^4\left({}^{1}D\right)3s$ satellite has peculiar properties that are analyzed in detail: We find a small monomer-cluster shift of the binding energy, but no splitting of the satellite in a bulk and a surface component. Final state mechanisms that could lead to this behavior, which differs significantly from the main valence photoelectron lines, are discussed.

Figure 1

Photoelectron spectra of atomic Ne (bottom) and mixtures of atomic Ne with Ne clusters (other traces). The cluster series was produced by varying the gas pressure and nozzle temperature. The mean cluster size $⟨N⟩$ is determined using a scaling law (see text for details). The spectra were recorded with a photon energy of $60.5\mathrm{eV}$. Assignments of the Ne 2p correlation satellites are taken from Ref. 7. For a better view of the satellite lines the spectral region from $48.8\text{to}58.2\mathrm{eV}$ is enlarged.

Figure 2

Spectrum of $2p$ correlation satellites from Ne clusters, inferred by subtracting the scaled atomic contribution from the topmost spectrum in Fig. 1.

Figure 3

Relative intensities of monomer and cluster photoelectron lines vs cluster size for the $2p^4\left({}^{1}D\right)3s$ satellite [panel (a), top] and the $2s$ main line [panel (b), bottom]. For the $2s$ main line, the decomposition in bulk and surface component is also given. The percentage of the satellite peak area develops proportionally to the sum of surface and bulk peak areas of the photoline.

Figure 4

(Color online) Photoemission spectra of Ne $2p^4\left({}^{1}D\right)3s$ satellites for four different average cluster sizes, $⟨N⟩=40$, $⟨N⟩=255$, $⟨N⟩=450$, and $⟨N⟩=550$. The spectra were recorded with photon energies of $60.5\mathrm{eV}$. The fit reveals two cluster satellite components [I–II, solid lines], which are tentatively assigned to a different local ordering in the cluster, as described in the text. The residuals (i.e., the difference between the data and the fit) are shown below the corresponding spectra.