High-resolution
mass spectra of helium droplets doped with gold
and ionized by electrons reveal He
n
Au+ cluster ions. Additional doping with heavy noble gases results
in Ne
n
Au+, Ar
n
Au+, Kr
n
Au+, and Xe
n
Au+ cluster ions.
The high stability predicted for covalently bonded Ar2Au+, Kr2Au+, and Xe2Au+ is reflected in their relatively high abundance. Surprisingly, the
abundance of Ne2Au+, which is predicted to have
zero covalent bonding character and no enhanced stability, features
a local maximum, too. The predicted size and structure of complete
solvation shells surrounding ions with essentially nondirectional
bonding depends primarily on the ratio σ* of the ion–ligand
versus the ligand–ligand distance. For Au+ solvated
in helium and neon, the ratio σ* is slightly below 1, favoring
icosahedral packing in agreement with a maximum observed in the corresponding
abundance distributions at n = 12. He
n
Au+ appears to adopt two additional solvation
shells of I
h symmetry, containing 20 and
12 atoms, respectively. For Ar
n
Au+, with σ* ≈ 0.67, one would expect a solvation
shell of octahedral symmetry, in agreement with an enhanced ion abundance
at n = 6. Another anomaly in the ion abundance at
Ar9Au+ matches a local maximum in its computed
dissociation energy.