FORMATION OF C60(-) AND C70(-) BY FREE-ELECTRON CAPTURE - ACTIVATION-ENERGY AND EFFECT OF THE INTERNAL ENERGY ON LIFETIME

Electron attachment to C60 and C70 yields long-lived (i.e. mass spectrometrically observable) anions C60- and C70- within a remarkably broad energy region (up to 13-14 eV) as already established in a previous experiment. Inspection of the low energy region reveals, however, that electron capture is characterized by an activation barrier of 240 meV for C60 close to the results of the previous FALP study and 200 meV for C70. Flight time measurements of the anions indicate that the lifetimes of C60- and C70- decrease exponentially with increasing internal energy in the range 8 less-than-or-equal-to E* less-than-or-equal-to 12 eV. For example, at 10 eV the lifetime is 90 mus for C60- and 300 mus for C70-. It is also established that the lifetime of both anions is controlled by electron emission (detachment).