Thermionic emission from fullerenes

Fullerenes in the gas phase, excited by a pulsed laser, exhibit thermionic emission. We analyze the time dependence of the ion yield of Cn+ in a mass spectrometer. By pulsing the extraction field of the ion lens, we are able to observe delayed ions formed as late as 50 μs after excitation by the 2nd, 3rd or 4th harmonic of a Q-switched YAG laser. The enhanced sensitivity of this new technique allows us to detect delayed ions not only from excited C60 and C70, but from all other even-sized clusters in the size range 36 ≤ n ≤ 70. Our results do not confirm the assertion that thermionic emission from C60 and C70 can be characterized by just 2 or 3 distinct rate constants. (author). 29 refs, 5 figs