ANOMALOUS ENRICHMENT OF C-2(-ABLATION OF GRAPHITE IN AR JET() IONS BYLASER)

The formation mechanisms of C-1(+), and C-2(+), and C-3(+) ions by las er ablation of graphite are investigated using time-of-flight (TOF) qu adrupole mass spectroscopy. The laser ablation is performed in conjunc tion with a pulsed Ar expansion to elucidate the third-body effect on the formation of the small carbon cluster ions. Drastic enhancement of the C-2(+) ion signal is observed by an increase of the local pressur e near the target, indicating that C-2(+) ions are efficiently formed by recombination of carbon atoms and subsequent ionization. The branch ing ratio of C-1(+), C-2(+), and C-3(+) ions and their mean translatio nal energies are different from those of neutrals. Also, the TOF spect ra for C-n(+) ions show multiple peak structures, which implies that d ifferent mechanisms are involved in the formation of C-n(+) ions. (C) 1998 American Institute of Physics.