Energetics and Structures of Charged Helium Clusters: Comparing Stabilities of Dimer and Trimer Cationic Cores

Abstract

We present accurate ab initio calculations of the most stable structures of He(n)(+) clusters in order to determine the more likely ionic core arrangements existing after reaching structural equilibrium of the clusters. Two potential energy surfaces are presented: one for the He(2)(+) and the other with the He(3)(+) linear ion, both interacting with one He atom. The two computed potentials are in turn employed within a classical structure optimization where the overall interaction forces are obtained within the sum-of-potentials approximation described in the main text. Because of the presence of many-body effects within the ionic core, we find that the arrangements with He(3)(+) as a core turn out to be energetically preferred, leading to the formation of He(3)(+)(He)(n-3) stable aggregates. Nanoscopic considerations about the relative stability of clusters with the two different cores are shown to give us new information on the dynamical processes observed in the impact ionization experiments of pure helium clusters and the importance of pre-equilibrium evaporation of the ionic dimers in the ionized clusters.

Insights Into Chemical Reactions at the Beginning of the Universe: From HeH+ to H3+

“…This has been done by using a fresh computational approach-by employing the ab initio nanoreactor (AINR). The simulations reveal the presence of unique dicationic helium chains of up to five atoms, which should act as a fillip for investigating the possibility of the presence of such species in helium clusters, which have received attention both from experimental and theoretical studies (Bieske and Dopfer, 2000;Marinetti et al, 2008;Oleksy et al, 2010). Our studies also confirm that HeH + was indeed the first molecule to be formed and that it played a vital role in the origin of H 3 + .…”

“…Previously, there have been some reports (Marinetti et al, 2008;Oleksy et al, 2010) with regard to the formation of mono-cationic He ion clusters. Our current AINR based dynamics study reveals that there is a possibility of the formation of a dicationic helium chain of up to five He atoms: He 3 2+ , He 4 2+ and He 5…”

Solvation of Intrinsic Positive Charge in Superfluid Helium

“…The more recent electronic structure calculations for small ground state He + n clusters have employed variants of the configuration interaction method (CI) or the coupled clusters theory (CC) with the latter including single (S), double (D) and perturbative triples excitations (T), and typically used a medium sized correlation consistent basis set. [25][26][27][28] The main aim of these studies has been to characterize the full potential energy surface for ground state He + 3 and to compute the bound He + 3 vibronic states with respect to the He + 2 + He dissociation channel. [25][26][27] From the perspective of the triatomic ion formation, the barrierless linear He + 2 -He approach leads directly to the formation of He + 3 .…”

“…Most importantly, it was observed that the addition of more He atoms around the ion followed approximately a pair-wise additive behavior such that the total interaction could be obtained simply by summing over the ion core -He pairs as well as the He -He pairs that do not belong to the ionic core. 28 Finally, we note the series of diatomics-in-molecules (DIM) studies of charged helium clusters, where the basic DIM method surprisingly breaks down for the relative simple He + 3 molecule. 8,[30][31][32] DIM is an attractive alternative for the computationally heavy traditional ab initio methods and is, for example, fast enough to be used in molecular dynamics work.…”

SF6+: Stabilizing Transient Ions in Helium Nanodroplets

“…In an undoped HND, the charge will be localized on He 2 + or He 3 + . 32 Upon pickup of SF 6 , the dopant and the charge will move toward each other through the superfluid medium; charge transfer will release ∼8.0 eV (see the Supporting Information ). Given the large (1.1 eV) energy that is channeled into the F + SF 5 + fragments upon vertical ionization, 21 and the disparity in the mass of F and He, whether the helium matrix can fully cage the products is questionable.…”