Kinetic energies of charged fragments resulting frommultifragmentation and asymmetric fission of the C60molecule in collisions with monocharged ions(2–130 keV)

Abstract

Multifragmentation and asymmetric fission (AF) of the C60 molecule inducedby H+,H2+,H3+and He+ions at medium collision energies (2–130 keV) areconsidered. Momenta and kinetic energies of Cn+ fragmentions (n = 1– 12)are deduced from an analysis of time-of-flight spectra. In multifragmentationprocesses, momenta are found to be approximatively constant when n > 2, abehaviour which explains that the most probable kinetic energy, as well as the width ofthe kinetic energy distributions, is found to be inversely proportional to the fragmentsize n;both momenta and kinetic energies are independent of the velocityand nature of the projectile, and hence of the energy deposit. Aspecific study of the AF shows that the kinetic energies of C2+, C4+ andC6+fragments are also independent of the collision velocity and projectile species; aquantitative agreement is found with values deduced from kinetic energy releasemeasurements by another group in electron impact experiments, and the observeddecrease when the mass of the light fragment increases is also reproduced.A quantitative comparison of AF and multifragmentation for the n = 2, 4and 6 fragment ions shows that kinetic energies in AF exceed that inmultifragmentation, a result which explains the oscillations observedwhen momenta or kinetic energies of fragments are plotted against then-value.The AF yield is also found to scale with the energy deposit in the collisionvelocity range extending below the velocity at the maximum of the electronicstopping power; except for protons, it remains negligible with respect tomultifragmentation as soon as the total energy deposit exceeds about 100 eV.