Communication: Dopant-induced solvation of alkalis in liquid helium nanodroplets

Renzler, Michael; Daxner, Matthias; Kranabetter, Lorenz; Kaiser, Alexander; Hauser, Andreas; Ernst, Wolfgang; Lindinger, Albrecht; Zillich, Robert E.; Scheier, P.; Ellis, Andrew M.

doi:10.1063/1.4967405

Cited by 31 publications

(37 citation statements)

References 33 publications

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“…Neutral cesium clusters are expected to reside on the surface of helium nanodroplets [32]. However, the addition of C60 which is electrophilic and highly polarizable will induce Csn clusters to dissolve in the droplet provided n > 1 [33]. .…”

Section: Discussionmentioning

confidence: 99%

“…For additional insight we now turn to other reports. Theoretical work has been limited so far to the lighter alkalis (with the exception of jellium-type calculations for C 60 fully coated with one or more layers of cesium [4,13], and recent calculations restricted to Cs monomer and dimers [33,34]). These studies reveal a delicate balance between Coulomb repulsion between atomic ions favoring uniform coverage, and metallic bonding favoring island formation [35].…”

Section: Discussionmentioning

confidence: 99%

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Adsorption of sodium and cesium on aggregates of C60

et al. 2016

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Abstract.We explore the formation of C60 sodium and C60 cesium complexes in superfluid helium nanodroplets. Anomalies in mass spectra of these doped droplets reveal anomalies in the stability of ions. (C60)mCs + n ions (m 6) are particularly abundant if they contain n = 6m + 1 cesium atoms; (C60)mCs 2+ n dications (m 3 or 5) are abundant if n = 6m + 2. These findings are consistent with the notion that alkali metal atoms (A) transfer their valence electrons into the three-fold degenerate lowest unoccupied orbital of C60, resulting in particularly stable C60A6 building blocks. However, (C60)4Cs 2+ n dications display an entirely different pattern; instead of an expected anomaly at n = 6 × 4 + 2 = 26 we observe a strong odd-even alternation starting at n = 6. Also surprising is the effect of adding one H2O or CO2 molecule to (C60)mCsn mono-or dications; anomalies shift by two units as if the impurity were acting as an acceptor for two valence electrons from the alkali metal atoms.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Adsorption of sodium and cesium on aggregates of C60

et al. 2016

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“…15,16 However, this poses a challenge, since one must find a way to combine ionized C 60 and methanol molecules at low temperature. Here we approach this problem by trapping the neutral molecules in liquid helium nanodroplets and then ionizing the system using electron ionization.…”

Section: Introductionmentioning

confidence: 99%

Electron ionization of helium droplets containing C₆₀ and alcohol clusters

Goulart

Zappa

Ellis

et al. 2017

Phys. Chem. Chem. Phys.

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aWe report a mass spectrometric investigation of (C 60 ) n clusters mixed with either methanol or ethanol clusters inside helium nanodroplets. The abundance of ion products produced by electron ionization shows marked differences compared with pure methanol/ethanol clusters without C 60 [M. Goulart, P. Bartl, A. Mauracher, F. Zappa, A. M. Ellis and P. Scheier, Phys. Chem. Chem. Phys., 2013, 15, 3577], where clusters containing in excess of a hundred alcohol monomers were observed. In contrast, under identical conditions concerning He droplet size and alcohol pickup pressure, only a small number of alcohol molecules become attached to the fullerene ions. Our results suggest that each fullerene cluster acts as a charge sink, which hampers alcohol cluster formation, as well as intra-cluster ion-molecule reactions. The appearance of specific 'magic number' peaks suggests an enhanced probability for the attachment of small alcohol rings to (C 60 ) n + clusters.

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“…In the case of HnC60Cs + , we first doped the helium droplets with fullerene and hydrogen which can only form neutral (H2)mC60 clusters with a purely statistical distribution and no odd numbered species. Cesium was added in a second pickup chamber and, since cesium is a heliophobic species [45][46][47][48], it resides preferentially on the surface of the droplet [49]. Thus, another ionization process is accessible, where cesium is ionized on the outside of the droplet via Penning ionization by He* [50], which is also a heliophobic species [51].…”

Section: Resultsmentioning

confidence: 99%

On enhanced hydrogen adsorption on alkali (cesium) doped C60 and effects of the quantum nature of the H2 molecule on physisorption energies

Kaiser

Renzler

Kranabetter

et al. 2017

International Journal of Hydrogen Energy

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Hydrogen storage by physisorption in carbon based materials is hindered by low adsorption energies. In the last decade doping of carbon materials with alkali, earth alkali or other metal atoms was proposed as a means to enhance adsorption energies, and some experiments have shown promising results. We investigate the upper bounds of hydrogen storage capacities of C60Cs clusters grown in ultracold helium nanodroplets by analyzing anomalies in the ion abundance that indicate shell closure of hydrogen adsorption shells. On bare C60 + , a commensurate phase with 32 H2 molecules was identified in previous experiments. Doping C60 with a single cesium atom leads to an increase in relative ion abundance for the first 10 H2 molecules, and the closure of the commensurate phase is shifted from 32 to 42 H2 molecules.Density functional theory calculations indicate that thirteen energetically enhanced adsorption sites exist, where six of them fill the groove between Cs and C60 and 7 are located at the cesium atom. We emphasize the large effect of the quantum nature of the hydrogen molecule on the adsorption energies, i.e. the adsorption energies are decreased by around 50% for (H2)C60Cs and up to 80% for (H2)C60 by harmonic zero-point corrections, which represent an upper bound to corrections for dissociation energies (De to D0) by the vibrational ground states. Five normal modes of libration and vibration of H2 physisorbed on the substrate contribute primarily to this large decrease in adsorption energies. A similar effect can be found for H2 physisorbed on benzene and is expected to be found for any other weakly H2-binding substrate. © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http:// creativecommons.org/licenses/by-nc-nd/4.0/

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Communication: Dopant-induced solvation of alkalis in liquid helium nanodroplets

Cited by 31 publications

References 33 publications

Adsorption of sodium and cesium on aggregates of C60

Adsorption of sodium and cesium on aggregates of C60

Electron ionization of helium droplets containing C₆₀ and alcohol clusters

On enhanced hydrogen adsorption on alkali (cesium) doped C60 and effects of the quantum nature of the H2 molecule on physisorption energies

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Communication: Dopant-induced solvation of alkalis in liquid helium nanodroplets

Cited by 31 publications

References 33 publications

Adsorption of sodium and cesium on aggregates of C60

Adsorption of sodium and cesium on aggregates of C60

Electron ionization of helium droplets containing C60 and alcohol clusters

On enhanced hydrogen adsorption on alkali (cesium) doped C60 and effects of the quantum nature of the H2 molecule on physisorption energies

Contact Info

Product

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Electron ionization of helium droplets containing C₆₀ and alcohol clusters