M. A. Lebeault

Electronic properties of mixed barium–oxygen clusters

Herein electronic structure as a function of cluster size has been probed through ionization potentials measurements in order to derive general trends in the evolution of the structure and stability of lithium oxide clusters LinOm. The structural evolution was investigated by varying progressively the oxygen rate in order to observe transitions from the metallic Lin to the ionic structure (Li2O)n. We have demonstrated that this structural transition splits into three specific ranges. This result, in contrast with the general behavior observed with other electronegative elements combined with alkaline or alkaline-earth metal clusters, but similar to what is known about BanOm and CsnOm, constitutes a signature of a specific role played by the oxygen atoms when included inside a metallic cluster.

Decay of C60 by delayed ionization and C2 emission: Experiment and statistical modeling of kinetic energy release

C(60) molecules highly excited in the nanosecond regime decay following ionization and dissociation by emitting a series of carbon dimers, as well as other small fragments if excitation is strong enough. The fragmentation mass spectrum and kinetic energy release of all charged fragments obtained in these experiments are interpreted within the framework of the Weisskopf theory, using a realistic Monte Carlo procedure in which the rates of all relevant decay channels are modeled using Arrhenius expressions. Comparison between the measurements and the simulated spectra allows the distribution of deposited energy to be accurately estimated. The dependence of the fragment kinetic energies on the laser fluence, found in the simulation but not observed in the experimental results, indicates that the small fragments are not necessarily emitted from small fullerenes resulting from C(60) by sequential decay. Rather, direct multifragmentation of C(60) is invoked to interpret the observed patterns. The possible role of post-ionization of neutral emitted fragments is discussed.