Cationic complexes of hydrogen with helium

Abstract

High-resolution mass spectra of helium nanodroplets doped with hydrogen or deuterium reveal that copious amounts of helium can be bound to H+, H2+, H3+, and larger hydrogen-cluster ions. All conceivable HenHx+ stoichiometries are identified if their mass is below the limit of ≈120 u set by the resolution of the spectrometer. Anomalies in the ion yields of He nHx+ for x=1, 2, or 3, and n≤30 reveal particularly stable cluster ions. Our results for HenH 1+ are consistent with conclusions drawn from previous experimental and theoretical studies which were limited to smaller cluster ions. The HenH3+ series exhibits a pronounced anomaly at n=12 which was outside the reliable range of earlier experiments. Contrary to findings reported for other diatomic dopant molecules, the monomer ion (i.e. H2+) retains helium with much greater efficiency than hydrogen-cluster ions. Trapping helium on hydrogen: Helium nanodroplets are doped with hydrogen or deuterium and subsequently ionized by electron impact. Cationic complexes of Hx+ (x=1, 2, 3) with up to 30 helium atoms are identified in the high-resolution mass spectra. Pronounced anomalies in the size dependence of their abundance indicate particularly stable helium-hydrogen complexes (see picture). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.