Event by event analysis of collision induced cluster ion fragmentation: sequential monomer evaporation versus fission reactions

IP

Direct observation of multi-ionization and multi-fragmentation in a high-velocity cluster-atom collision

IPMWe report the direct observation of the multi-ionization of the $H_{21}^+$ hydrogen cluster in a single collision with a helium atom at 60 keV/u. Up to quadruple ionization of the cluster was observed and new multi-fragmentation channel were detected. Moreover, the results show two different fragmentation processes of doubly charged $H-{21}^{2+}$ clusters: emission of an $H_2^+$ dimer, or emission of an $H-3^+$ trimer after rearrangement in the cluster prior to fragmentation

Multifragmentation d'agregats induite par collisions a haute vitesse

pas de resum

Absolute cross sections for the dissociation of hydrogen cluster ions in high-energy collisions with helium atoms

Absolute dissociation cross sections are reported for Hn+ clusters of varied mass (n=3,5,,35) following collisions with He atoms at 60 keV/amu. Initial results have been published previously for a smaller range of cluster sizes [Ouaskit et al., Phys. Rev. A 49, 1484 (1994)]. The present extended study includes further experimental results, reducing the statistical errors associated with the absolute cross sections. The previously suggested quasilinear dependence of the Hn+ dissociation cross sections upon n is developed with reference to expected series of geometrical shells of H2 molecules surrounding a H3+ core. Recent calculations identify n=9 as corresponding to the first closed H2 shell [e.g., tich et al., J. Chem. Phys. 107, 9482 (1997)]. Recurrence of the distinct characteristics observed in the dissociation-cross-section dependence upon cluster size around n=9 provides the basis for the presently proposed subsequent closed shells at n=15, 21, 27, and 33, in agreement with the calculations of Nagashima et al