COLLISION OF ALKALI IONS WITH C-60 C-70 - INSERTION, THERMIONIC EMISSION, AND FRAGMENTATION/

Interactions of Li+, Na+, and K+ with C60 molecules have been studied over the collision energy range from 0 to 150 eV. For Li+ and Na+, ins ertion of the alkali to form the endohedral [Li @ C60]+ and [Na @ C60] + species is observed, with appearance energies of approximately 6 and approximately 18 eV, respectively. At higher collision energies sever al processes are observed. For Na+, the hot [Na @ C60]+ appears to rel ax mainly by loss of C2 units from the fullerene cage, yielding [Na @ C60-2n]+. For [Li @ C60]+, escape of Li+ dominates over C2 loss. For K +, very little [K @ C60]+ is observed, and the main endohedral species observed are fragMents [K @ C60-2n]+ (n = 1-7), which begin to appear at approximately 40 eV. Pure fullerene fragment ions (C60+-2n) are al so observed, with cross sections that increase sharply at approximatel y 30 eV for all three projectile ions. These ions are believed to resu lt primarily from thermionic emission of collisionally excited neutral s. For K+, we also examined collisions with C70, obtaining results sim ilar to those for C60. Changes in the endohedral insertion mechanism w ith projectile size are discussed, as is the competition between C2 ev aporation, thermionic emission, and IR emission.