The fragmentation upon electron impact ionization of Ar4He1000 is investigated by means of mixed quantum–classical dynamics simulations. The Ar4+ dopant dynamics is described by a surface hopping method coupled with a diatomics-in-molecules model to properly take into account the multiple Ar4+ electronic surfaces and possible transitions between them. Helium atoms are treated individually using zero-point averaged dynamics, a method based on the building of an effective He–He potential. Fast electronic relaxation is observed from less than 2 ps to ∼30 ps, depending on initial conditions. The main fragments observed are Ar2+Heq and Ar3+Heq (q ≤ 1000), with a strong contribution of the bare Ar2+ ion, and neither Ar+ nor Ar+Heq fragments are found. The smaller fragments (q ≤ 50) are found to mostly come from ion ejection, whereas larger fragments (q > 500) originate from long-term ion trapping. Although the structure of the trapped Ar2+ ions is the same as in the gas phase, trapped Ar3+ and Ar4+ are rather slightly bound Ar2+Ar and Ar2+ArAr structures (i.e., an Ar2+ core with one or two argon atoms roaming within the droplet). These loose structures can undergo geminate recombination and release Ar3+Heq or Ar4+Heq (q ≤ 50) in the gas phase and/or induce strong helium droplet evaporation. Finally, the translational energy of the fragment center of mass was found to be suitable to provide a clear signature of the broad variety of processes at play in our simulations.

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