Evaporation of covalent clusters: Unimolecular decay of energized size-selected carbon cluster ions (Cn+, 5=n=100)
Por:
Radi P.P., Hsu M.T., Brodbelt-Lustig J., Rincon M., Bowers M.T.
Publicada:
1 ene 1990
Resumen:
The unimolecular decay of energized size-selected carbon clusters (C n+,5 ? n ? 100) is investigated. The clusters are produced in a laser-generated plasma on the surface of a graphite rod. Directly extracted cations that decay on a ?s time scale are probed in a double-focusing, reverse-geometry mass spectrometer. The unimolecular decomposition rates are extracted from metastable fraction measurements. We observe a dramatic discontinuous increase in the decay rate constant as a function of cluster size around mass C30+ (factor of 5 to 10). Additionally, low rate constants, relative to the neighbors, are found for C50+, C60+, and C70 +. The results are rationalized by postulating a phase transition from small "rigid" clusters for n < 30 to larger "molten" entities for n > 30. In this model local deviations in rate constant reflect the thermodynamic stabilities of the clusters. A further consequence of this model is that "magic" numbers in the mass spectrum originate primarily from the intrinsic stability of the clusters with respect to evaporation and not from a kinetic growth mechanism. © 1990 American Institute of Physics.
Filiaciones:
Radi P.P.:
Department of Chemistry, University of California, Santa Barbara, CA 93106, United States
Hsu M.T.:
Department of Chemistry, University of California, Santa Barbara, CA 93106, United States
Brodbelt-Lustig J.:
Department of Chemistry, University of California, Santa Barbara, CA 93106, United States
Rincon M.:
Department of Chemistry, University of California, Santa Barbara, CA 93106, United States
Bowers M.T.:
Department of Chemistry, University of California, Santa Barbara, CA 93106, United States
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