title: Direct experimental evidence for a negative heat capacity in the liquid-to-gas phase transition in hydrogen cluster ions: backbending of the caloric curve.
abstract: By selecting specific decay reactions in high-energy collisions (60 keV/amu) of hydrogen cluster ions with a helium target (utilizing event-by-event data of a recently developed multicoincidence experiment) and by deriving corresponding temperatures for these microcanonical cluster ensembles (analyzing respective fragment distributions), we are able to construct caloric curves for H+3(H2)(m) cluster ions (6<or=m<or=14). All individual curves and the mean of these curves show a backbending in the plateau region, thus constituting direct evidence for a negative microcanonical heat capacity in the liquid-to-gas transition of these finite systems.
authors.affiliation: Institut de Physique Nucléaire de Lyon, IN2P3-CNRS et Université Claude Bernard, 43 boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France.
authors.forename: F
authors.initials: F
authors.lastname: Gobet
authors.forename: B
authors.initials: B
authors.lastname: Farizon
authors.forename: M
authors.initials: M
authors.lastname: Farizon
authors.forename: M J
authors.initials: MJ
authors.lastname: Gaillard
authors.forename: J P
authors.initials: JP
authors.lastname: Buchet
authors.forename: M
authors.initials: M
authors.lastname: Carré
authors.forename: P
authors.initials: P
authors.lastname: Scheier
authors.forename: T D
authors.initials: TD
authors.lastname: Märk