title: Mass Spectrometric Observation of Doubly Charged Alkaline-Earth Argon Ions.
abstract: Doubly charged diatomic ions MAr(2+) where M=Mg, Ca, Sr or Ba have been observed by mass spectrometry with an inductively coupled plasma ion source. Abundance ratios are quite high, 0.1 % for MgAr(2+) , 0.4 % for CaAr(2+) , 0.2 % for SrAr(2+) and 0.1 % for BaAr(2+) relative to the corresponding doubly charged atomic ions M(2+) . It is assumed that these molecular ions are formed through reactions of the doubly charged metal ions with neutral argon atoms within the ion source. Bond dissociation energies (D0 ) were calculated and agree well with previously published values. The abundance ratios MAr(+) /M(+) and MAr(2+) /M(2+) generally follow the predicted bond dissociation energies with the exception of MgAr(2+) . Mg(2+) should form the strongest bond with Ar [D0 (MgAr(2+) )=124 to 130 kJ mol(-1) ] but its relative abundance is similar to that of the weakest bound BaAr(2+) (D0 =34 to 42 kJ mol(-1) ). The relative abundances of the various MAr(2+) ions are higher than those expected from an argon plasma at T=6000 K, indicating that collisions during ion extraction reduce the abundance of the MAr(2+) ions relative to the composition in the source. The corresponding singly charged MAr(+) ions are also observed but occur at about three orders of magnitude lower intensity than MAr(2+) .
authors.affiliation: Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir Prelog Weg 1, CH-8093, Zurich, Switzerland. bodo@inorg.chem.ethz.ch.
authors.forename: Bodo
authors.initials: B
authors.lastname: Hattendorf
authors.affiliation: Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir Prelog Weg 1, CH-8093, Zurich, Switzerland.
authors.forename: Bianca
authors.initials: B
authors.lastname: Gusmini
authors.affiliation: Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir Prelog Weg 1, CH-8093, Zurich, Switzerland.|Solvias AG, Römerpark 2, CH-4303, Kaiseraugst, Switzerland.
authors.forename: Ladina
authors.initials: L
authors.lastname: Dorta
authors.affiliation: Ames Laboratory U. S. Department of Energy, Department of Chemistry, Iowa State University, Ames, IA, 50011, USA.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Houk
authors.affiliation: Laboratory of Inorganic Chemistry, ETH Zurich, Vladimir Prelog Weg 1, CH-8093, Zurich, Switzerland.
authors.forename: Detlef
authors.initials: D
authors.lastname: Günther
keywords: alkaline earth metals; inductively coupled plasma mass spectrometry; mass spectrometry; molecular ions; noble gases