Unraveling the Metastability of C_<i>n</i>²⁺ (<i>n</i> = 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 Cn2+ (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 Cn–1+ + C+. During C22+ → C+ + C+, significant kinetic energy release (∼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 12C22+ dications are either in weakly bound 3Πu and 3Σg– states, quickly dissociating under the intense electric field, or in a deeply bound electronic 5Σu– state with lifetimes >180 ps