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

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

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

Studies of charging mechanisms in impurity-helium condensates by means of impedance spectroscopy and current spectroscopy

A new simple experimental technique has been elaborated to test applicability of impedance spectroscopy for studying processes during destruction of impurity-helium condensates. Combination of methods of optical spectroscopy, impedance spectroscopy and current spectroscopy to study the destruction processes of impurityhelium condensates has been applied for the first time. Experimental data have demonstrated a rather good sensitivity of the technique and proved formation of charged clusters during a destruction stage of impurity-helium condensates.Просту експериментальну методику розроблено та успішно випробувано для використання можливостей спектроскопії імпедансу при дослідженні процесів на стадії руйнування зразків домішково-гелієвих конденсатів. Вперше використано комбінацію методів спектроскопії імпедансу, струмової спектроскопії та оптичної спектроскопії для дослідження руйнування домішково-гелієвих конденсатів. Отримані результати показали високу чутливість нової методики та підтвердили появу зарядів (заряджених нанокластерів) на стадії руйнування домішково-гелієвих конденсатів. Ключові слова: нанокластери, доміПростая экспериментальная методика разработана и успешно опробована для использования возможностей спектроскопии импеданса при исследовании процессов на стадии разрушения образцов примесь-гелиевых конденсатов. Впервые использована комбинация методов спектроскопии импеданса, токовой спектроскопии и оптической спектроскопии для исследования разрушения примесь-гелиевых конденсатов. Полученные результаты показали высокую чувствительность новой методики и подтвердили появление зарядов (заряженных нанокластеров) на стадии разрушения примесьгелиевых конденсатов