Hydrogenating atomic coinage metal cations (group 11) with H2 on charged He droplets (T<10 K) doped with metal Atoms: Early stages, ligation energies, core structures, group variations, and relativistic effects

Experimental mass-spectrometric results are reported which demonstrate that ionized helium nanodroplets (at T < 10 K) doped with the coinage metal atoms M = Cu, Ag or Au, and then exposed to molecular hydrogen, provide an abundance of singly and multiply hydrogenated coinage metal cations M + (H 2 ) n and MH + (H 2 ) n with n up to 25 and beyond. We explore here the information provided by observed distributions in the measured intensities of these ligated ions with n = 1–6 and use ab initio quantum chemical calculations to extract fundamental insights into variations in ligation energies and structures with increasing H 2 ligation and going down the Periodic Table (M + = Cu + , Ag + and Au + ) with an eye on the role of relativistic contributions to the ligation energies expected with the increasing nuclear charge of M + . “Magic” numbers of H 2 additions with relatively high intensity are apparent among the first 5, especially the first 2, H 2 additions. Very substantial relativistic enhancements of the third over the second-row ligation energies were computed, especially for Au + : 83 % and 60 % respectively, for the first two H 2 ligands intimately bonded to Au + , and 19 % and 67 % respectively, for the addition of the first two H 2 ligands to AuH + . Relativistic enhancements for the addition of a third H 2 ligand and beyond were found to be essentially negligible. • Charged He nano-droplets doped with coinage metal M atoms yield H 2 ligated M + and MH + . • “Magic” numbers of H 2 additions of relatively high intensity are seen among the first 5. • Calculations provide core structures for M + (H 2 ) n and MH + (H 2 ) n with n = 1 to 6. • Calculated ligation energies show variations down the Group with second-row minima. • Calculated H 2 ligation energies increase for Au + and AuH + due to relativistic effects.