Dynamic localization of inner-shell excitations in free atomic and molecular clusters

Experimental and theoretical results on core-excited variable-size atomic and molecular clusters are reported. Rydberg excitations in rare gas clusters serve to study core-hole localization phenomena in weakly bound atomic systems. Specifically, 3s excited variable size argon clusters exhibit distinct shifts of the 3s" border=0 src="/.dejavu/.tact/lib1/art410/pcdata/html_gif/charset.gif/bam.gif"np window resonances converging to the Ar 3s ionization threshold. These shifts are assigned on the basis of the quasiatomic approach, considering the influence of nearest neighbors as well as long range effects on the Ar 3s" border=0 src="/.dejavu/.tact/lib-1/art410/pcdata/html_gif/charset.gif/bam.gif"np Rydberg series. Experimental results on 1s-excited nitrogen- and carbon monoxide-clusters show almost identical spectra compared to the bare molecules and the solid. A significant blue-shift of the sigma* shape-resonance relative to the isolated molecule is found in homogeneous nitrogen clusters and in the solid, whereas no shifts are observed in CO-clusters. These results are rationalized by using the quasiatomic approach in terms of differences in dynamic localization of core-excitations in the regime of sigma* shape-resonances.