Resonant X-Ray Absorption of Neon Clusters: The Influence of Cluster Size on the Character of Core Excited States

First resonant $K$-shell absorption spectra of atomic clusters covering the size range from the atom to the solid are reported. Discrete absorption into Rydberg states as well as the near edge ionization continuum (XANES/EXAFS) of neon clusters ($N\ensuremath{\approx}15\ensuremath{-}4000$) is investigated with excellent spectral resolution. Shifts and splittings of the absorption features ($1s\ensuremath{\rightarrow}3p,4p$) provide information on local properties of the different atomic sites. Besides identifying surface and bulk contributions we observe how the character of a transition changes from a Rydberg orbital in a small cluster into a bulk excitation in larger systems.