title: Atomically resolved phase transition of fullerene cations solvated in helium droplets.
abstract: Helium has a unique phase diagram and below 25 bar it does not form a solid even at the lowest temperatures. Electrostriction leads to the formation of a solid layer of helium around charged impurities at much lower pressures in liquid and superfluid helium. These so-called 'Atkins snowballs' have been investigated for several simple ions. Here we form HenC60+complexes with n exceeding 100 via electron ionization of helium nanodroplets doped with C60. Photofragmentation of these complexes is measured by merging a tunable narrow-bandwidth laser beam with the ions. A switch from red- to blueshift of the absorption frequency of HenC60+on addition of He atoms at n=32 is associated with a phase transition in the attached helium layer from solid to partly liquid (melting of the Atkins snowball). Elaborate molecular dynamics simulations using a realistic force field and including quantum effects support this interpretation.
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Kuhn
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Renzler
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: J
authors.initials: J
authors.lastname: Postler
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Ralser
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Spieler
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Simpson
authors.affiliation: Leiden Observatory, University of Leiden, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands.
authors.forename: H
authors.initials: H
authors.lastname: Linnartz
authors.affiliation: Leiden Observatory, University of Leiden, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands.
authors.forename: A G G M
authors.initials: AG
authors.lastname: Tielens
authors.affiliation: Department of Physics and Astronomy/Centre for Planetary Science and Exploration (CPSX), The University of Western Ontario, London, Ontario, Canada N6A 3K7.|SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, California 94043, USA.
authors.forename: J
authors.initials: J
authors.lastname: Cami
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Mauracher
authors.affiliation: Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain.|Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain.|Institute for Advanced Research in Chemical Sciences (IAdChem), Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain.|Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain.|Institute for Advanced Research in Chemical Sciences (IAdChem), Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Alcamí
authors.affiliation: Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain.|Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain.|Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Martín
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: M K
authors.initials: MK
authors.lastname: Beyer
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: R
authors.initials: R
authors.lastname: Wester
authors.affiliation: Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Lindinger
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, Innsbruck A-6020, Austria.
authors.forename: P
authors.initials: P
authors.lastname: Scheier