He tagging maps copper cluster ion shapes

Helium nanodroplet mass spectrometry of 63Cu clusters shows magic He shells that match computed binding sites, including twisted-X Cu5+.

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How were Cu cluster ions grown?

Pickup of monoisotopic 63Cu into charged helium nanodroplets.

Why use isotope-enriched 63Cu?

To assign He_mCu_n+ up to n = 10 and m = 100 without isotope clutter.

What He shell closes on Cu+?

m = 6, an octahedron.

How strongly is the first He bound to Cu+?

About 40 meV each before ZPE.

What geometry is assigned to Cu5+?

Twisted-X; smallest 3D structure identified.

What experimental magic number supports Cu5+?

Strong enhancement at m = 4 He.

How much higher is the trigonal bipyramid?

About 70 meV above twisted-X; planar X is a TS.

What theory level optimized the clusters?

MP2 after tests vs coupled cluster for structures and energies.

Droplet temperature for growth?

Ultracold, around 0.4 K, atom-by-atom onto a cold core.

Do anions bind more He?

Yes, more He on anions at nearly the same evaporation pressure.

Why are anion magic numbers at m = 7, 9 shaky?

Possible isobaric N2Cu_n+ and (H2O)2Cu_n+ impurities.