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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, домі Простая 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.

We have studied thermo-stimulated luminenscence and electron emission of nitrogen films and nanoclusters containing free radicals of atomic nitrogen. Thermo-stimulated electron emission from N2 nanoclusters was observed for the first time. Thermo-stimulated luminescence spectra obtained during the destruction of a N2–He sample 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 luminescence intensity and electron current in both systems points to the important role of ionic species in relaxation cascades. Sublimation of solid helium shells isolating nitrogen nanoclusters is a trigger for the initiation of thermo-stimulated luminescence and electron emission in these nitrogen–helium condensates.

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.

1. Section 2.1, second paragraph, fifth line. Sentence is correct as follows: The α′-group corresponds to the electronic transition N(2D → 4S) accompanied by a simultaneous vibrational excitation v = 0 → v = 1 in the neighbouring N2(X1Σ+ g ) molecule. 2. Section 2.2, line 12: a-group and g-line are corrected as α-group and γ -line. 3. Section 3, second paragraph, line 6: W3 −u (v′′ = 4) → A3Σ+ u (v′ = 0–4) is corrected to W3 u(v′′ = 4) → A3Σ+ u (v′ = 0–4) 4. Section 3, second paragraph, line 16: W3 −u is corrected to W3 u 5. Updated Ref. 2 is as follows: V.V. Khmelenko, I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, D.M. Lee, Low Temp. Phys. 38, 871 (2012).

We present optical spectra of impurity-helium condensates during the process of their formation by injection of gas mixtures N2-Rg-He (Rg=Ne, Kr) into bulk superfluid helium after passing through a RF discharge. Atomic lines of He, Ne, Kr, N, O atoms as well as bands (1+ and 2+ systems of N2) are present in the spectral range 320–1100 nm studied in these experiments. We also detected spectra emitted by the samples during their destruction, stimulated by warming through the temperature range 1.5–15 K The luminescence spectra of the N-N2-He and N-N2-Ne-He samples contain only intense N(2D-4S) (α-group) and O(1D-1S) (β-group) lines. For the N-N2-Ne-He sample we observed the transformation of spectra of the α-group. In thermo-stimulated luminescence spectra of the N-N2-Kr-He samples, the intense β-group of O atoms and M-bands of NO molecules were found. Differences in the spectra obtained during destruction of N-N2-Ne-He and N-N2-Kr-He samples may be explained by a different shell structure of the nanoclusters formed during sample preparation.

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.