  Helium nanodroplets are doped with cesium and molecular hydrogen and
subsequently ionized by electrons. Mass spectra reveal H$_x$Cs$^{+}$ 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 H$_2$Cs$^+$. 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, 44
to the formation of three concentric, solid-like solvation shells of
icosahedral symmetry around Cs$^+$. Preliminary density functional theory
calculations for n $\le$ 14 are reported as well.
