The submersion of sodium clusters in helium nanodroplets: Identification of the surface → interior transition

Lan, Lukas An der; Bartl, Peter; Leidlmair, Christian; Schöbel, Harald; Jochum, Roland; Denifl, Stephan; Märk, T.D.; Ellis, Andrew M.; Scheier, P.

doi:10.1063/1.3610388

Cited by 92 publications

(84 citation statements)

References 36 publications

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“…The midpoint of this transition is reasonably close to a recent theoretical prediction of n = 78 for submersion into helium. The lack of a sharp surface-interior transition, in contrast to previous observations for Na n , 9 suggests that the location of K n on the surface or inside the helium droplet is nearly isoenergetic over a significant range of n. Because n needs to be much larger for K n than for Na n to defeat the more unfavorable Pauli repulsion, the addition or removal of a single K atom has a proportionately smaller effect on the solvation energetics for K n than on those for Na n , thus blurring the surface-interior transition.…”

Section: Discussioncontrasting

confidence: 55%

“…The experimental apparatus and procedure were recently described in detail, 9 so only a brief account of key aspects is provided here. Neutral helium droplets were formed by supersonic expansion of 4 He (99.9999% purity) through a 5-μm aperture in a platinum disk.…”

Section: Methodsmentioning

confidence: 99%

“…9 This work, which focused on sodium clusters, employed electron impact mass spectrometry. By recording mass spectra as a function of electron energy, it was shown that small sodium clusters ionize mainly through Penning ionization.…”

Section: Introductionmentioning

confidence: 99%

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Submersion of potassium clusters in helium nanodroplets

et al. 2012

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Small alkali clusters do not submerge in liquid helium nanodroplets but instead survive predominantly in high spin states that reside on the surface of the nanodroplet. However, a recent theoretical prediction by Stark and Kresin [Phys. Rev. B 81, 085401 (2010)], based on a classical description of the energetics of bubble formation for a fully submerged alkali cluster, suggests that the alkali clusters can submerge on energetic grounds when they exceed a critical size. Following recent work on sodium clusters, where ion yield data from electron impact mass spectrometry was used to obtain the first experimental evidence for alkali cluster submersion, we report here on similar experiments for potassium clusters. Evidence is presented for full cluster submersion at n > 80 for K n clusters, which is in good agreement with the recent theoretical prediction. In an additional observation, we report "magic number" sizes for both K n + and K n 2+ ions derived from helium droplets, which are found to be consistent with the jellium model.

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Section: Discussioncontrasting

confidence: 55%

Section: Methodsmentioning

confidence: 99%

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Submersion of potassium clusters in helium nanodroplets

et al. 2012

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“…Full details of the apparatus have been given previously 12 and so only a brief account is provided here. Helium nanodroplets were produced by expanding highly pure (99.9999%) gaseous helium at high pressure (21-23 bars) and a controlled temperature (8.8-9.6 K) through a 5 µm pinhole into a vacuum.…”

Section: Methodsmentioning

confidence: 99%

The interaction of He⁻ with fullerenes

Mauracher

Daxner

Huber

et al. 2015

The Journal of Chemical Physics

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The effects of interactions between He − and clusters of fullerenes in helium nanodroplets are described. Electron transfer from He − to (C 60 ) n and (C 70 ) n clusters results in the formation of the corresponding fullerene cluster dianions. This unusual double electron transfer appears to be concerted and is most likely guided by electron correlation between the two very weakly bound outer electrons in He − . We suggest a mechanism which involves long range electron transfer followed by the conversion of He + into He 2 + , where formation of the He-He bond in He 2 + releases sufficient kinetic energy for the cation and the dianion to escape their Coulombic attraction. By analogy with the corresponding dications, the observation of a threshold size of n ≥ 5 for formation of both (C 60 ) n 2− and (C 70 ) n 2− is attributed to Coulomb explosion rather than an energetic constraint. We also find that smaller dianions can be observed if water is added as a co-dopant. Other aspects of He − chemistry that are explored include its role in the formation of multiply charged fullerene cluster cations and the sensitivity of cluster dianion formation on the incident electron energy. C

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“…22) the clusters can now move inside a helium droplet. [26] When both (SF 6 ) m and Na n clusters are combined in a helium droplet the substantial polarizability of SF 6 will create an attractive (dispersive) interaction with Na n . We therefore anticipate that clusters smaller than Na 22 will now relocate to the droplet interior when (SF 6 ) m is also present and, although we have no specific evidence, this may even occur for atomic sodium.…”

Section: Methodsmentioning

confidence: 99%

Electron‐Driven Self‐Assembly of Salt Nanocrystals in Liquid Helium

Daxner¹,

Denifl²,

Scheier³

et al. 2014

Angewandte Chemie

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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 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) n Na + and (NaF) n F À . 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 À anions, which then initiate anionic chemistry by electron transfer.Neutral and ionic alkali-metal halide clusters have been widely studied, both experimentally and theoretically. Part of the motivation to study these species is to see if the threedimensional structures of the crystalline salts are retained in relatively small clusters. Such information can be derived from mass spectrometry through the observation of anomalously intense peaks (so-called magic number features). Several methods have been used to produce alkali-metal halide cluster ions in the gas phase, including sputtering, [1] laser ablation, [2] electrospray, [3] and ion-molecule reactions in a flowing afterglow. [4] The general finding, whether detecting cations or anions, is that enhanced signal intensity is seen for cluster ions (magic-number ions) of composition consistent with one or more complete unit cells. On these grounds it is reasonable to suppose that the cluster ions adopt structures based on the normal crystalline structure of the extended solid.Herein we show that it is possible to form alkali-metal halide clusters by reactions between clusters of sodium and SF 6 in liquid helium nanodroplets. The low intrinsic temperature (ca. 0.4 K) and the rapid cooling of dopants in these droplets, [5] which is assisted by the high thermal conductivity of superfluid helium, should inhibit chemical reactions. However, reaction between sodium and SF 6 can be triggered by electron impact on the droplet, leading to a rich range of cationic and anionic salt clusters. Particularly surprising is that self-assembly into structures based on the unit cell of NaF occurs even when the chemistry is initiated inside a liquid helium nanodroplet.The two reagents were added separately to the helium droplets, with sodium vapor coming from an oven containing solid sodium while the SF 6 was supplied from a gas cylinder. SF 6 was added to the first pick-up cell and sodium vapor to the second pick-up cell. The partial pressures of the dopants were set so that the most probable process was pick-up of a relatively small number of dopant atoms/molecules. However, the statistical nature of the pick-up process means that, in practice, clusters spanning a relatively wide range of sizes were generated. Reaction products derive...

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The submersion of sodium clusters in helium nanodroplets: Identification of the surface → interior transition

Cited by 92 publications

References 36 publications

Submersion of potassium clusters in helium nanodroplets

Submersion of potassium clusters in helium nanodroplets

The interaction of He⁻ with fullerenes

Electron‐Driven Self‐Assembly of Salt Nanocrystals in Liquid Helium

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The submersion of sodium clusters in helium nanodroplets: Identification of the surface → interior transition

Cited by 92 publications

References 36 publications

Submersion of potassium clusters in helium nanodroplets

Submersion of potassium clusters in helium nanodroplets

The interaction of He− with fullerenes

Electron‐Driven Self‐Assembly of Salt Nanocrystals in Liquid Helium

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Product

Resources

About

The interaction of He⁻ with fullerenes