Deuterium atoms and molecules in nanoclusters of molecular deuterium

Abstract

Impurity-helium solids created by injecting deuterium atoms and molecules into superfluid 4 He have been studied via x-ray-diffraction and electron-spin-resonance ͑ESR͒ techniques. X-ray-diffraction measurements show that these solids are highly porous gel-like structures consisting of D 2 clusters with the characteristic cluster size of 90Ϯ30 Å. The densities of D 2 molecules in the samples are 7ϫ10 20 -3ϫ10 21 cm Ϫ3 . Each of the D 2 clusters are either partially or totally surrounded by thin layers of adsorbed helium which may play an important role in preventing the coalescence of the clusters into larger crystallites of solid D 2 . Using ESR, we find that average concentrations of D atoms of order 1ϫ10 18 cm Ϫ3 can be achieved in our samples. Measurements of the ground-state spectroscopic parameters and relaxation times of atomic deuterium show that the D atoms reside in the D 2 clusters. The combined x-ray and ESR data show that local concentrations of D atoms as large as 2ϫ10 19 cm Ϫ3 are obtained in our experiments. The highly porous deuterium nanostructures studied in this work are promising for the production of high concentrations of ultracold neutrons and for significant nuclear polarization of D 2 molecules by the ''brute force method'' at low temperatures.

Neon in carbon nanopores: wetting, growth mechanisms, and cluster structures

“…Clusters grown inside pores obey the growth mechanisms typical of confined geometry and demonstrate the absolute prevalence of structures with the five-fold symmetry [7][8][9]. Such structures were earlier observed in essentially different experiments [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] with the only one common feature, i.e., the limited number of interacting atoms during growth.…”

On charged impurity structures in liquid helium

“…Nevertheless, the model did not allow us to explain the photostimulated luminescence of IHC samples submerged in bulk He II. Moreover, the model was not confirmed by structural studies of IHCs revealed nanoclusters as building units of the condensates [10][11][12].…”

“…Such particles and systems have found many different applications: visualization of flows and quantum vortices in superfluid helium [2][3][4]; study of energy transfer phenomena in liquid helium [5]; development of new high-energy density materials [6][7][8]; investigation of tunneling reactions of hydrogen isotopes in impurity-helium condensates [9]; structural studies of rare gas, molecular deuterium and nitrogen nanoclusters [10][11][12]; study of cold neutron interaction with watergels [13,14]; synthesis of metallic nanowires in superfluid helium [15,16]. Laser ablation of metallic target in solid helium-4 allows to create so-called icebergs (helium crystals doped with metallic particles) remaining metastable below the melting curve [17,18].…”

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

“…This method not only allowed exceptionally high concentrations of stabilized atoms (up to 10% atomic nitrogen in N-N 2 samples) [3] but also provided for a variety of significant experiments. Optical spectroscopy [4][5][6][7][8][9], ESR [10][11][12][13][14][15][16][17][18], x-ray diffraction [19][20][21][22][23] and ultrasound techniques [24][25][26][27] were used to characterize these samples and to determine why free radical stabilization was so effective. It was found that the samples of impurity helium condensates formed inside superfluid helium have a porous structure composed of nanoclusters of impurity species with characteristic size of order 5 nm [19].…”