Absolute Charge Transfer and Fragmentation Cross Sections inHe2+−C60Collisions

Abstract

We have determined absolute charge transfer and fragmentation cross sections in He2++C60 collisions in the impact-energy range 0.1-250 keV by using a combined experimental and theoretical approach. We have found that the cross sections for the formation of He+ and He0 are comparable in magnitude, which cannot be explained by the sole contribution of pure single and double electron capture but also by contribution of transfer-ionization processes that are important even at low impact energies. The results show that multifragmentation is important only at impact energies larger than 40 keV; at lower energies, sequential C2 evaporation is the dominant process.

Determination of Energy-Transfer Distributions in Ionizing Ion-Molecule Collisions

“…The form of the distribution shown in Fig. 2 is qualitatively similar to those obtained by fitting theoretical fragmentation probabilities to experimental measured branching ratios in small carbon clusters [27] and fullerenes [33,35], in which the energy distribution was the fitting parameter, thus showing that the present results are also compatible with previous empirical estimations. Notice that, although the set of accessible target states can, in principle, be different in photoionization and collision processes, due to the different conservation rules that can apply in each case, this is not a problem in the present work because the absence of any symmetry in the molecular target does not restrict the number of accessible states in either process.…”

“…Collisions at closer impact parameters can explain the extended tail towards larger deposited energy [27,32,33]. Penetrating trajectories are associated with large deposit energy of several tens of eV [33]. However, in the present interaction of 48 keV O 6þ with thymidine, peripheral collisions leading to small energy transfer are dominating.…”

“…The energy distribution increases smoothly up to a maximum around 2-3 eV and then it extends up to 8 eV and likely also above this energy, in a region not investigated in the present PEPICO experiments. Collisions at closer impact parameters can explain the extended tail towards larger deposited energy [27,32,33]. Penetrating trajectories are associated with large deposit energy of several tens of eV [33].…”

“…Notice that, although the set of accessible target states can, in principle, be different in photoionization and collision processes, due to the different conservation rules that can apply in each case, this is not a problem in the present work because the absence of any symmetry in the molecular target does not restrict the number of accessible states in either process. Moreover, the single-electron capture, which is the dominant process at impact energies considered in this work, is not accompanied by excitation of target and projectile electrons [33,35]. Therefore, one can safely assume that the mass spectra resulting from the collision involves the same target states as the PEPICO spectra.…”

Multiple electron capture, excitation, and fragmentation inC6+−C60collisions

“…C 2 emission from C q+ 60 is found to dominate when q 2 while C + 2 emission dominates when q 5, in agreement with the present and previous experimental results. DOI Over the past decades, fullerenes have been extensively studied by means of various excitation and ionization agents, such as photons [1][2][3], electrons [4][5][6][7][8], ions [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], or laser pulses [25][26][27][28][29][30]. It has been demonstrated that hot fullerene ions produced in these interactions may cool down by electron emission [29,[31][32][33], radiative decay [34,35], or by statistical fragmentation processes [36][37][38][39].…”