title: Ion-molecule reactions of ammonia clusters with C60 aggregates embedded in helium droplets.
abstract: Helium nanodroplets are co-doped with C(60) and ammonia. Mass spectra obtained by electron ionization reveal cations containing ammonia clusters complexed with up to four C(60) units. The high mass resolution of Δm/m≈ 1/6000 makes it possible to separate the contributions of protonated, unprotonated and dehydrogenated ammonia. C(60) aggregates suppress the proton-transfer reaction which usually favors the appearance of protonated ammonia cluster ions. Unprotonated C(x)(NH(3))(n)(+) ions (x = 60, 120, 180) exceed the abundance of the corresponding protonated ions if n < 5; for larger values of n the abundances of C(60)(NH(3))(n)(+) and C(60)(NH)(n-1)NH(4)(+) become about equal. Dehydrogenated C(60)NH(2)(+) ions are relatively abundant; their formation is attributed to a transient doubly charged C(60)-ammonia complex which forms either by an Auger process or by Penning ionization following charge transfer between the primary He(+) ion and C(60). The abundance of C(x)NH(3)(+) and C(x)NH(4)(+) ions (x = 120 or 180) is one to two orders of magnitude weaker than the abundance of ions containing one or two additional ammonia molecules. However, a model involving evaporation of NH(3) or NH(4) from the presumably weakly bound C(x)NH(3)(+) and C(x)NH(4)(+) ions is at odds with the lack of enhancement in the abundance of C(120)(+) and C(180)(+). Mass spectra of C(60) dimers complexed with water complement a previous study of C(60)(H(2)O)(n)(+) recorded at much lower mass resolution.
authors.affiliation: Institut für Ionenphysik und Angewandte Physik and Center for Molecular Biosciences Innsbruck, Leopold Franzens Universität, Technikerstr. 25, A-6020 Innsbruck, Austria.
authors.forename: Harald
authors.initials: H
authors.lastname: Schöbel
authors.forename: Christian
authors.initials: C
authors.lastname: Leidlmair
authors.forename: Peter
authors.initials: P
authors.lastname: Bartl
authors.forename: Abid
authors.initials: A
authors.lastname: Aleem
authors.forename: Michaela
authors.initials: M
authors.lastname: Hager
authors.forename: Olof
authors.initials: O
authors.lastname: Echt
authors.forename: Tilmann D
authors.initials: TD
authors.lastname: Märk
authors.forename: Paul
authors.initials: P
authors.lastname: Scheier
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D006371:Helium / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D013058:Mass Spectrometry; D053758:Nanoparticles / Q000737:chemistry; D011522:Protons; D014867:Water / Q000737:chemistry
chemical_list: D037741:Fullerenes; D007477:Ions; D011522:Protons; D014867:Water; D006371:Helium; D000641:Ammonia; C069837:fullerene C60