Cationic Complexes of Hydrogen with Helium

High‐resolution mass spectra of helium nanodroplets doped with hydrogen or deuterium reveal that copious amounts of helium can be bound to H + , H 2 + , H 3 + , and larger hydrogen‐cluster ions. All conceivable He n H x + 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 n H x + for x =1, 2, or 3, and n ≤30 reveal particularly stable cluster ions. Our results for He n H 1 + are consistent with conclusions drawn from previous experimental and theoretical studies which were limited to smaller cluster ions. The He n H 3 + 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. H 2 + ) retains helium with much greater efficiency than hydrogen‐cluster ions.