RESUMO
Absolute cross sections for double-electron transfer in H(-) + H(+) collisions have been measured for center-of-mass energies from 0.5 to 12 keV. Clear oscillations in the cross section are observed shedding new light on earlier measurements. Calculations based on a diabatic approach are shown to reproduce this behavior, but require a larger diabatic ion-pair splitting than previously assumed.
RESUMO
Fullerenes are a direct link between atoms with discrete electronic energy levels and solids with a band structure and a well-defined surface. In this Letter, we report on the first ever experiment on resonant electron transfer in collisions between two fullerene ions. Total cross sections have been measured for the reaction C+60+C2+60-->C2+60+C+60 at center-of-mass energies ranging from 27 to 69 keV. Surprisingly, within the error bars, these cross sections are identical to the respective cross sections for C+60+C60 measured by Rohmund and Campbell [J. Phys. B 30, 5293 (1997)]]. We show that the experimental data for both collision systems are very well reproduced by a quantum mechanical treatment of the reaction based on the concept of hole particles and the polarizability of the fullerene molecule.
RESUMO
Experimental measurements and theoretical calculations are carried out for the electron-impact ionization of Sm(12+). The low energy region of the single ionization cross section for Sm(12+) is found to be dominated by contributions from the indirect process of excitation autoionization. At about 1.0 keV strong resonance features are found in the experimental crossed-beam measurements performed in scan mode at high resolution. Theoretical calculations confirm that the high energy experimental features are due to deep-core dielectronic capture followed by sequential double Auger decay. The discovery of these unusual high energy resonances in single and multiple ionization opens the door for future systematic studies of how heavy atomic ions with deep inner-shell vacancies achieve final stabilization.
RESUMO
Cross sections for the electron-impact multiple ionization and fragmentation of negatively charged fullerene ions C(-)(n) ( n = 60, 70) to C(q+)(n-m) ( q = 1,2,3 and m = 0,2,4) have been measured for electron energies up to 1 keV. In the case of pure ionization all threshold energies are about 10 eV higher than the values expected. This shift, however, is not observed for the fragment ions. The experimental data indicate that there is no strong electron-electron interaction between the incident electron and the attached electron. A novel ionization mechanism is proposed which can be expected to be valid for all negatively charged molecular or cluster ions which are able to shield the attached electron from the incident electron.
RESUMO
The C2 fragmentation of fullerene ions C(q+)(60) (q = 1,2,3) induced by electron impact was studied for the first time. The cross sections for the loss of a C2 fragment indicate the presence of two different processes. At low electron energies the projectile electron leads to the direct excitation of the giant plasmon resonance. At electron energies larger than 100 eV the fragmentation of the fullerene ions can be described as an unsuccessful ionization. Only this second part of the cross section shows a dependence on the charge state q of the precursor ion.
