Entrance Channel X-HF (X=Cl, Br, and I) Complexes studied by High-Resolution Infrared Laser Spectroscopy in Helium Nanodroplets

Rotationally resolved infrared spectra are reported for halogen atom - HF free radical complexes formed in helium nanodroplets. An effusive pyrolysis source is used to dope helium droplets with Cl, Br and I atoms, formed by thermal dissociation of Cl$_2$, Br$_2$ and I$_2$. A single hydrogen fluoride molecule is then added to the droplets, resulting in the formation of the X-HF complexes of interest. Analysis of the resulting spectra confirms that the observed species have $^2\Pi_{3/2}$ ground electronic states, consistent with the linear hydrogen bound structures predicted from theory. Stark spectra are also reported for these species, from which the permanent electric dipole moments are determined.Comment: 41 pages, 16 figures, 5 table

Electron-driven self-assembly of salt nanocrystals in liquid helium

The self-assembly of salt nanocrystals from chemical reactions inside liquid helium is reported for the first time. Reaction is initiated by an electron impacting a helium nanodroplet containing sodium atoms and SF[suubscript 6] molecules, leading to preferential production of energetically favorable structures based on the unit cell of crystalline NaF. These favorable structures are observed as magic number ions (anomalously intense peaks) in mass spectra and are seen in both cationic and anionic channels in mass spectra, for example, (NaF)[subscript n]Na[superscript +] and (NaF)[subscript n]F[superscript −]. In the case of anions the self-assembly is not directly initiated by electrons: the dominant process involves resonant electron-induced production of metastable electronically excited He[superscript −] anions, which then initiate anionic chemistry by electron transfer

Energetics and structures of charged helium clusters: comparing stabilities of dimer and trimer cationic cores

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