Direct experimental evidence for a negative heat capacity in the liquid-to-gas phase transition in hydrogen cluster ions: backbending of the caloric curve.
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.
Gobet
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F
Institut de Physique Nucléaire de Lyon, IN2P3-CNRS et Université Claude Bernard, 43 boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France.
Farizon
B
B
Farizon
M
M
Gaillard
M J
MJ
Buchet
J P
JP
Carré
M
M
Scheier
P
P
Märk
T D
TD