Cs+ Solvated in Hydrogen-Evidence for Several Distinct Solvation Shells

Helium nanodroplets are doped with cesium and molecular hydrogen and subsequently ionized by electrons. Mass spectra reveal HxCs+ ions that contain as many as 130 hydrogen. atoms. Two features in the spectra are striking: First, the abundance of ions with an odd number of hydrogen atoms is very low; the abundance of HCs+ is only 1% that of H2Cs+. The dominance of even-numbered species is in stark contrast to previous studies of pure or doped hydrogen cluster ions. Second, the abundance of (H-2)(n)Cs+ features anomalies at n = 8, 12, 32, 44, and 52. Guided by previous work on ions, solvated in hydrogen and helium, We assign the anomalies,at n = 12, 32, and 44 to the formation of three concentric, solid-like solvation shells of icosahedral symmetry around,Cs+. Preliminary density functional theory calculations for n <= 14 are reported as well.