Multiply Charged Neon Clusters: Failure of the Liquid Drop Model?

Abstract

We have analyzed the stability and fission dynamics of multiply charged neon cluster ions. The critical sizes for the observation of long-lived ions are n2=284 and n3=656 for charge states 2 and 3, respectively, a factor 3 to 4 below the predictions of a previously successful liquid-drop model. The preferred fragment ions of fission reactions are surprisingly small (2<or=n<or=5); their kinetic energy distributions peak at 200 meV or below. The size of these fragments and their average kinetic energies are much less than predicted by the liquid-drop model.

Coulomb fission in multiply charged molecular clusters: Experiment and theory

“…What is slightly surprising about the +4 results is the very small size of some of the fragment ions; however, the experiments by Mähr et al 7 on the fragmentation of multiply charged neon clusters showed a preference for dimer and trimer ions, and the imaging experiments of Hoener et al 16 showed that monomer and dimer ions were also generated during the fission of neon dication clusters. Finally, the calculations of Miller et al 38 on multiply charged clusters of Lennard-Jones particles show the ejection of individual charged particles from comparatively small clusters, but also provide evidence of a transition to more symmetric fission as the clusters increase in size.…”

“…11 If fission results in just two fragments, then the Coulomb repulsion that accompanies their separation should lead to a significant release of kinetic energy, and estimates from previous experiments range from 0.2 to 1 eV. 1,6,7,13 However, it has been shown earlier that a simple point charge calculation of the kinetic energy release expected for a dication cluster composed of a dielectric material gives a very unrealistic estimate for the location of the two charges. 11 Apart from earlier studies of triply charged CO2 and NH3 clusters, 1,8 neither of which included any size-dependent data, there have been no recorded examples of the delayed Coulomb fission of multiply charged molecular clusters.…”

“…[1][2][3][4][5][6][7] To date, those multiply charged molecular clusters that have been the subject of experimental measurement have exhibited a lower size limit, below which they become unstable due to Coulomb repulsion between the resident charges. 1 There have been numerous experimental attempts to observe the process of Coulomb fission that should accompany the instability of molecular clusters, 1,4,5,6,8 and although charge separation has been observed in photoexcited multiply charged clusters of metal atoms, 9 until recently, 10,11 attempts to observe similar processes in size-selected molecular clusters have not been particularly successful.…”

“…Given the timescales on which many typical mass spectrometers operate (~ 10 -5 s), fission is the most obvious outcome; however, until recently a definitive identification of such a process in a size-selected cluster had not been forthcoming. 10,11 Attempts to capture events on a much shorter experimental time scale include a novel deflection method adopted by Mähr et al 7 and an imaging experiment by Hoener et al, 16 which has succeeded in distinguishing between Coulomb explosion and fission, and has also generated scattering patterns for each type of event.…”

Communication: Delayed asymmetric Coulomb fission of molecular clusters: Application of a dielectric liquid-drop model

“…Experimental measurements of the acquired kinetic energy during the latter subprocess ranges from 0.2 to 1 eV. 5,8,11 If the complete process is not spontaneous, it is referred to as a delayed Coulomb fission. Apart from early measurements on triply charged CO 2 and NH 3 clusters, 3,12 there have been no recorded examples of delayed Coulomb fission of molecular clusters.…”