Delayed ionization of laser desorbed C60 molecules following 193 nm photoexcitation

Delayed ionization of C60 on the microsecond timescale has been investigated following 193 nm excitation of infrared laser desorbed molecules. Biexponential decay of the delayed ion signal indicates the autoionization of two kinetically distinct superexcited states. The lifetimes of these states were determined to be 5 ± 1 μs and 0·8 ± 0·2 μs; their excitation energies are estimated to lie in the range 20–30 eV. These results are compared with the predictions of the Richardson-Dushman and Klots models of thermionic emission. The observation of a dependence of delayed ion intensity on desorption conditions is interpreted in terms of a thermally induced phase change during the desorption process.