Abstract
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.
Highlights
S ince first detected in the tail of a comet in 1882,1 pure carbon clusters have attracted considerable attention from physicists and chemists, which has translated into a vast amount of literature.[2−7] Carbon is one of the most abundant elements in the universe
There is experimental work reporting the detection of the Cn2+ (n = 2−4) cluster ions using time-of-flight (TOF) mass spectroscopy,[34,35] but the stability and fragmentation dynamics of the clusters have not been explored in detail
For fragments resulting from in-flight dissociations of cluster ions, their TOF values and their measured mass-to-charge state ratios differ from their counterparts directly emitted from the emitter’s surface
Summary
Both long-lived and excited C52+ ions by high-velocity collisions of 10 MeV C5+ ions with a He target.[32]. For fragments resulting from in-flight dissociations of cluster ions, their TOF values and their measured mass-to-charge state ratios differ from their counterparts directly emitted from the emitter’s surface. For homolytical dissociation of dications with an even number of carbon atoms such as C22+ and C42+, that is, C2n2+ → Cn+ + Cn+, the true mass-to-charge state ratios of the two fragments, Cn+ and the parent ion, C2n2+, are the same, and the KER is the only cause of a difference in the TOF, which translates into a difference in the measured mass-tocharge state ratio, Δm, between both fragments, giving rise to a dissociation track in the ion-correlation histogram Because in this case θA + θB = 180°, that is, cos(θA) = −cos(θB), we can eliminate the KER and angle dependence from eq 1 to get Figure 2.
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