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Fig. 6.13. M/q (mass divided by charge) spectrum resulting from the fragmentation of 200-keV C60 projectiles colliding with H2 molecules in the gas-phase. The right- and left-hand parts of the spectrum reflect singly and doubly charged fragments, respectively, which appear to be replicas of one another [6.46],

30 40 50

30 40 50

Fig. 6.13. M/q (mass divided by charge) spectrum resulting from the fragmentation of 200-keV C60 projectiles colliding with H2 molecules in the gas-phase. The right- and left-hand parts of the spectrum reflect singly and doubly charged fragments, respectively, which appear to be replicas of one another [6.46],

P,{m) for the evaporation of m carbon pairs in a time interval t after a collision is where ^ is the evaporation lifetime, while the total probability for the evaporation of m carbon pairs integrated over time is where p = f2/(*i + h)i *n which t2 is the characteristic lifetime of the rift in the C60 molecule. The results of Fig. 6.14 show that for collisions of C^ with a hydrogen molecule H2, the time t2 that the C6f0 molecular ion is open is about twice the characteristic time ij for emission of the m carbon pairs (and t2 — 3i, for the He target), independent of the incident energy of the Cg0 ion, although the average m value increases rapidly with increasing ion energy and mass of the target species [6.46]. Referring to Fig. 6.14, we see that the yield for m = 5 (corresponding to C<|0) is exceptionally large, indicative of the special stability of the Cj, species. The special stability of C50 is related to its structure, which is like that of C60, but with five fewer hexagons around the belt of the molecule, just as C70 has five additional hexagons around its belt.

Fig. 6.14. Fragment-peak intensities as a function of the number m of pairs of carbon atoms (C2) that are lost from an energetic Q0 ion upon collision with hydrogen and helium gas molecules [6.46], uj >-

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