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          Institute: MPI für Festkörperforschung     Collection: FKF Publikationen 2002     Display Documents

ID: 7134.0, MPI für Festkörperforschung / FKF Publikationen 2002
Structural transition in (C60)n clusters
Authors:Branz, W.; Malinowski, N.; Enders, A.; Martin, T. P.
Date of Publication (YYYY-MM-DD):2002
Title of Journal:Physical Review B
Issue / Number:9
Sequence Number of Article:094107
Review Status:Peer-review
Audience:Not Specified
Abstract / Description:The structure of (C-60)(n) clusters (n=1-150) was investigated
by heating them to definite temperatures in a helium bath
(heating cell) with subsequent characterization in a time-of-
flight mass spectrometer. The intensity anomalies in the
resulting mass spectra reflect particularly stable
configurations that resisted evaporation. However, the set of
enhanced peaks (magic numbers) turned out to be temperature
dependent. Clusters heated to a moderate temperature of 490 K
yielded mass spectra indicating the presence of icosahedral
structures that can be characterized by a set of unusually
strong peaks, namely n=13, 19, 23, 26, 35, 39, 43, 46, 49, 55,
55+3m, 116, 125, 131, 137, and 147 (m=1-14). Based on constant-
temperature molecular dynamics simulations it could be
concluded that these icosahedra represent metastable structures
that had not yet attained thermal equilibrium on the
experimental time scale (t(s)=0.5 ms). Only when the (C-60)(n)
clusters were heated to appreciably higher temperatures they
could reach thermodynamical equilibrium, manifested by a
thermally induced structural transition into close-packed
structures, decahedral structures and structures based on the
98-Leary tetrahedron. Thus, mass spectra of clusters heated to
600 K demonstrate the new set of magic numbers, n=38, 48, 58,
61, 64, 68, 71, 75, 77, 84, 89, 91, 96, and 98. Additionally,
the experimental arrangement used allows both charged and
neutral (C-60)(n) clusters to be studied. Thereby, it was
possible to show that the structure of large (C-60)(n) clusters
is insensitive to their charge state (-/n/+), disproving a
hypothesis that has been discussed in the literature for
several years. The heating cell was also used to study the
thermally induced dissociation in the fullerene dimers (C-
60)(2), (C-70)(2), and (C-60)(2)(+). The dissociation energies
were determined to be 0.275 eV, 0.313 eV, and 0.37 eV,
respectively (+/-0.08 eV).
External Publication Status:published
Document Type:Article
Communicated by:Michaela Asen-Palmer
Affiliations:MPI für Festkörperforschung
External Affiliations:; Max Planck Inst Festkorperforsch, Heisenbergstr 1, D-70569 Stuttgart, Germany
; Bulgarian Acad Sci, Cent Lab Photoproc, BG-1040 Sofia, Bulgaria
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