Electron-impact detachment and dissociation of C-4(-) ions

CRYRING was used to study collision processes between an electron and a neg ative ion cluster C-4(-). The total detachment cross sections for the produ ction of the neutral 4C, 3C, 2C, and C fragments were measured. The cross s ections for pure detachment, and for detachment plus dissociation leading t o the production of C-3+C, 2C(2), and C-2+2C were extracted using a grid. I t was found that the pure detachment process overwhelmingly dominates all o ther fragmentation processes. The threshold location for the detachment cha nnel is found to be around 6.0 eV. Although the doubly charged negative ion C-4(2-) has received little previous attention, a defined near-threshold r esonance observed in the detachment cross section curve, has been associate d with the short-lived state C-4(2-) (0.7 fs lifetime). (C) 2001 American I nstitute of Physics.