Dissociation channels of multiply charged van der Waals clusters

We have analyzed the reaction channels for the delayed, unimolecular dissociation of multiply charged clusters made from CO₂ and C₂{H}₄$. The smallest observable triply and quadruply charged clusters feature a large probability for fission into at least two charged fragments. The size distribution of heavy, doubly charged fragments from (CO₂{)}ₙ³⁺$, 109{}n{}123, has been analyzed in detail and shows a strong peak at 92% of the precursor size. Delayed fission of doubly charged clusters, however, does not occur on the time scale of the experiment, which is 10{}t{}100 {μ}s with respect to ionization. A simple model, based on a liquid-drop approximation, is proposed. It allows us to calculate the height of the fission barrier for any given precursor ion and fission channel from readily available bulk data. Calculated critical sizes are presented for two-, three-, and fourfold charged clusters of 28 different van-der-Waals--bound or hydrogen-bonded compounds; they agree reasonably well with experimental values. The model also accounts for the strongly asymmetric fission reaction of triply charged CO₂ clusters, and for the strong size dependence of their fission rate.