ESR studies of nitrogen atoms stabilized in aggregates of krypton–nitrogen nanoclusters immersed in superfluid helium

Mao, Shun; Boltnev, R. E.; Khmelenko, V. V.; Lee, D. M.

doi:10.1063/1.4765092

Cited by 17 publications

(15 citation statements)

References 41 publications

(52 reference statements)

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“…1). It is worth noting that the states C 5 Π u and W 3 − u can be formed by recombination of N( 4 S) and N( 2 D) atoms, which are present in high concentrations in impurity-helium condensates (up to 5 × 10 19 N( 4 S) atoms per cm 3 in krypton-helium samples [4] and a large amount of N( 2 D) atoms manifests in the spectra detected due to the very intense α-group).…”

Section: Discussionmentioning

confidence: 99%

“…Stabilization of radicals occurs mostly on the surface of the impurity nanoclusters, separated from each other by absorbed helium shells. The evaporation of helium atoms adsorbed on the impurity nanocluster surfaces starts a trigger mechanism for initiation of free radical recombination in impurity-helium condensates [2][3][4]. Such a trigger mechanism gives rise to chemical reactions during IHC sample warm-up for temperatures of 6-12 K. Intense recombinations of the stored radicals (nitrogen atoms in our case) create high concentrations of excited atoms and molecules.…”

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confidence: 96%

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Energy Release Channels During Destruction of Impurity-Helium Condensates

et al. 2012

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Injection of an impurity-helium gas jet passed through a radiofrequency discharge into a volume of superfluid helium leads to the growth of nanoclusters of impurity species which form impurity-helium condensates (IHCs). IHCs are porous materials with very low impurity density (∼10 20 cm −3 ). High average concentrations of stabilized free radicals can be achieved on the large total surface (∼100 m 2 /cm 3 ) of impurity nanoclusters. Warming of the IHCs leads to the destruction of the samples and formation of excited atoms and molecules as a consequence of the recombination of stabilized free radicals. We studied the influence of the nitrogen content in neon-helium and krypton-helium gas mixtures on the thermoluminescence spectra accompanying the destruction of the IHC samples, which were formed by using these gas mixtures. The energy release channels in the IHC samples were revealed from analysis of the thermoluminescence spectra.

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Section: Discussionmentioning

confidence: 99%

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confidence: 96%

Energy Release Channels During Destruction of Impurity-Helium Condensates

et al. 2012

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“…This allows us to determine the flux of nanoclusters to be 2•10 13 s -1 in the process of condensation of our nitrogen-helium gas mixture N 2 :He = 1:100 which has a flux 10 19 s -1 . Each nanocluster contains on average 50 nitrogen atoms, which reside mostly on the surfaces of these nanoclusters [17]. Usually during the process of their injection into He II, the nanoclusters collide inside superfluid helium and nitrogen atoms from the adjacent nano-cluster strands can meet each other and recombine.…”

Section: Discussionmentioning

confidence: 99%

“…During these measurements, the nanoclusters continued to enter into the bulk He II inside the rotating beaker. Nitrogen atoms stabilized on the surfaces of nanoclusters [17] provide an excellent opportunity for visualization of the process of capturing nanoclusters into vortex cores. When two nanoclusters are captured into a vortex core, they can collide and two nitrogen atoms residing on the surfaces of these nanoclusters can then recombine, starting processes which lead to luminescence of nitrogen atoms in nanoclusters.…”

Section: Introductionmentioning

confidence: 99%

Rotationally induced luminescence of nanoclusters immersed in superfluid helium

McColgan

Sheludiakov

Rentzepis

et al. 2019

Low Temperature Physics

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We studied the influence of rotation speed of a beaker containing superfluid helium (He II) on the intensity of luminescence of collections of nanoclusters immersed in He II. We observed an increase in the α-group emission of nitrogen atoms ( 2 D→ 4 S transition) in nanoclusters which correlated with the increasing of rotational speed of the beaker. Increasing luminescence was also observed by increasing the concentration of molecular nitrogen in the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. We suggest that this effect is caused by the change of the density of quantum vortices in He II initiated by variation of rotational speed of the beaker. When the density of the vortices is increased, the probability for the nanoclusters to become trapped in the vortex cores is also increased. The collisions in the vortex cores of trapped nanoclusters with nitrogen atoms stabilized mostly on the surfaces of the nanoclusters initiate the recombination of nitrogen atoms resulting in luminescence.

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“…[24] In our experiments, nitrogen atoms were captured mainly on the surface of the molecular nitrogen nanoclusters. [25] The average concentration of nitrogen atoms in nitrogenhelium condensates may be as high as 10 19 cm −3 . [26] EXPERIMENTAL APPARATUS…”

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confidence: 99%