Stabilization of H and D atoms in krypton–helium nanocondensates

Impurity–helium condensates formed by krypton nanoclusters containing atoms and molecules of hydrogen isotopes have been studied via an electron spin resonance (ESR) technique. Analysis of the ESR spectra has shown that most of the H and D atoms reside on the surfaces of Kr nanoclusters. Very large average concentrations have been obtained for H atoms (1.2·10¹⁹ cm⁻³) and D atoms (3.3·10¹⁹ cm⁻³) in these experiments. For the highest concentration of D atoms stabilized in the Kr–He sample, line narrowing has been observed. Exchange tunneling reactions have been studied in Kr–He sample containing H and D atoms

On charged impurity structures in liquid helium

The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warmup of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium

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

Impurity–helium condensates (IHCs) containing nitrogen and krypton atoms immersed in superfluid ⁴He have been studied via a CW electron spin resonance (ESR) technique. The IHCs are gel-like aggregates of nanoclusters composed of impurity species. It was found that the addition of krypton atoms to the nitrogen–helium gas mixture used for preparation of IHCs increases efficiency of stabilization of nitrogen atoms. We have achieved high average (5·10¹⁹ cm⁻³) and local (2·10²¹ cm⁻³) concentrations of nitrogen atoms in kryptonnitrogen–helium condensates. The analysis of ESR lines shows that three different sites exist for stabilization of nitrogen atoms in krypton-nitrogen nanoclusters. Nitrogen atoms are stabilized in the krypton core of nanoclusters, in the nitrogen molecular layer which covers the Kr core and on the surface of the nanoclusters. High concentrations of nitrogen atoms achieved in IHCs provide an important step in the search for magnetic ordering effects at low temperatures

A high-resolution infrared spectroscopic investigation of the halogen atom-HCN entrance channel complexes solvated in superfluid helium droplets

Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\Sigma_{1/2}$ and $^{2}\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, motivated by preliminary spectroscopic evidence for the di-radical Br-HCCCN-Br complex. Spectra for the corresponding molecular halogen HCN-X$_{2}$ complexes are also presented.Comment: 20 pages, 15 figures, 6 tables, RevTe

Optical spectroscopy and current detection during warm-up and destruction of impurity–helium condensates

New experimental results on detection of optical spectra and ion currents during destruction of impurity–helium condensates (IHCs) have been obtained. It is shown that emission during IHC sample destruction is accompanied by current pulses, pressure peaks and temperature changes. The molecular bands of excimer molecules XeO* are assigned to molecules stabilized in films of molecular nitrogen covering the heavier cores of impurity clusters which form impurity–helium condensates

Dynamics of thermoluminescence spectra of impurity– helium condensates containing stabilized nitrogen and oxygen atoms

The results of investigations of thermoluminescence dynamics during destruction of neon–helium and krypton–helium condensates containing stabilized nitrogen and oxygen atoms are presented. Spectra of the thermoluminescence of a krypton–helium condensate contained bands of N and O atoms and NO molecules. The intensities of the bands in these spectra were found to increase simultaneously during destruction processes in the temperature range 1.5–15 K. Observation of the NO molecules provides clear evidence for chemical reactions in the nanoclusters comprising the sample at low temperatures. Destruction of neon–helium samples occurred in two stages. During the first stage the α-group of N atoms surrounded by Ne and N₂ molecules dominated the spectra. During the second stage, the spectra contained intense bands of N and O atoms stabilized in a molecular nitrogen matrix. The unusual characteristics of the thermoluminescence spectra were observed, and their changes were explained in terms of the shell structure of impurity nanoclusters which comprised the impurity–helium condensates

Paramagnetic Attraction of Impurity-Helium Solids

Impurity-helium solids are formed when a mixture of impurity and helium gases enters a volume of superfluid helium. Typical choices of impurity gas are hydrogen deuteride, deuterium, nitrogen, neon and argon, or a mixture of these. These solids consist of individual impurity atoms and molecules as well as clusters of impurity atoms and molecules covered with layers of solidified helium. The clusters have an imperfect crystalline structure and diameters ranging up to 90 angstroms, depending somewhat on the choice of impurity. Immediately following formation the clusters aggregate into loosely connected porous solids that are submerged in and completely permeated by the liquid helium. Im-He solids are extremely effective at stabilizing high concentrations of free radicals, which can be introduced by applying a high power RF dis- charge to the impurity gas mixture just before it strikes the super fluid helium. Average concentrations of 10(exp 19) nitrogen atoms/cc and 5 x 10(exp 18) deuterium atoms/cc can be achieved this way. It shows a typical sample formed from a mixture of atomic and molecular hydrogen and deuterium. It shows typical sample formed from atomic and molecular nitrogen. Much of the stability of Im-He solids is attributed to their very large surface area to volume ratio and their permeation by super fluid helium. Heat resulting from a chance meeting and recombination of free radicals is quickly dissipated by the super fluid helium instead of thermally promoting the diffusion of other nearby free radicals

On charged impurity structures in liquid helium

The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warmup of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium

Comparative study of thermostimulated luminescence and electron emission of nitrogen nanoclusters and films

We have studied thermostimulated luminenscence and electron emission of nitrogen films and nanoclusters containing atomic nitrogen free radicals. Thermostimulated electron emission from N₂ nanoclusters was ob-served for the first time. Thermostimulated luminescence spectra obtained during N₂–He sample destruction are similar to those detected from N₂ films pre-irradiated by an electron beam. This similarity reveals common mechanisms of energy transfer and relaxation. The correlation of the luminescence intensity and the electron cur-rent in both systems points to the important role of ionic species in relaxation cascades. A sublimation of solid helium shells isolating nitrogen nanoclusters is a trigger for the initiation of thermostimulated luminescence and electron emission in these nitrogen–helium condensates

Ecosystem approach to fisheries management in the Barents Sea [presentation]

Management strategies for commercial marine species in northern ecosystems. Proceedings of the 10th Norwegian-Russian Symposium. Bergen, 27-29 August 2003