We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (${\mathrm{C}}_n^{-}$ , n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV ${\mathrm{C}}_2^{-}$ molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s ± 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10⁻¹⁴ mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.

We report on the production and study of stable, highly charged droplets of superfluid helium. Using a novel experimental setup we produce neutral beams of liquid helium nanodroplets containing millions of atoms or more that can be ionized by electron impact, mass-per-charge selected, and ionized a second time before being analyzed. Droplets containing up to 55 net positive charges are identified and the appearance sizes of multiply charge droplets are determined as a function of the charge state. We show that the droplets are stable on the millisecond timescale of the experiment and decay through the loss of small charged clusters, not through symmetric Coulomb explosions.

We present experimental evidence for the dominance of prompt single-atom knockout in fragmenting collisions between large polycyclic aromatic hydrocarbon cations and He atoms at center-of-mass energies close to 100 eV. Such nonstatistical processes are shown to give highly reactive fragments. We argue that nonstatistical fragmentation is dominant for any sufficiently large molecular system under similar conditions.

We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of ${\mathrm{C}}_{60}$ fullerenes. Surprisingly, $\mathrm{C}_{119}{}^{+}$ and $\mathrm{C}_{118}{}^{+}$ are the dominant molecular fusion products. We use molecular dynamics simulations to show that $\mathrm{C}_{59}{}^{+}$ and $\mathrm{C}_{58}{}^{+}$ ions—effectively produced in prompt knockout processes with ${\mathrm{He}}^{2+}$—react rapidly with ${\mathrm{C}}_{60}$ to form dumbbell $\mathrm{C}_{119}{}^{+}$ and $\mathrm{C}_{118}{}^{+}$. Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.