Unraveling the Metastability of Cn2+ (n=2-4) Clusters

Pure carbon clusters have received considerable attention for a long time. However, fundamental questions, such as what the smallest stable carbon cluster dication is, remain unclear. We investigated the stability and fragmentation behavior of C-n(2+) (n = 2-4) dications using state-of-the-art atom probe tomography. These small doubly charged carbon cluster ions were produced by laser-pulsed field evaporation from a tungsten carbide field emitter. Correlation analysis of the fragments detected in coincidence reveals that they only decay to C-n-1(+) + C+. During C-2(2+) -> C+ + C+ significant kinetic energy release (similar to 5.75-7.8 eV) is evidenced. Through advanced experimental data processing combined with ab initio calculations and simulations, we show that the field-evaporated diatomic C-12(2)2+ dications are either in weakly bound (3)Pi(u) and (3)Sigma(-)(g) states, quickly dissociating under the intense electric field, or in a deeply bound electronic (5)Sigma(-)(u) state with lifetimes >180 ps.