Search for doubly charged negative ions of small carbon clusters

A search has been conducted for dianions of small carbon clusters Cn2− (2 ≤ n ≤ 8) formed by laser ablation of graphite. A multicoincidence time-of-flight technique has been used to monitor fragment ion-pairs produced in dianion decay. No evidence is found for C22− dianions. However, detection of anion-pairs Cn−−Cn− (n > 1) provides evidence for higher-n (n > 2) cluster dianions which exhibit a preference for symmetrical decay. Ab initio computations of potential energy curves have been carried out for C22− dianion states; results indicate too short a lifetime against autodetachment for detection in our experiments.