Structure of Molecular Nitrogen Nanoclusters Containing Stabilized Nitrogen Atoms

Impurity-helium condensates (IHCs) formed by injecting the discharge products of gaseous mixtures of helium atoms and nitrogen molecules into bulk superfluid \(^{4}\) $_{}^4$ He at temperature 1.5 K, were studied by X-band electron spin resonance. IHCs consists of collections of \(\text {N}_2\) ${\text{N}}_2$ nanoclusters which form aerogel-like structure inside bulk HeII. It was found that \(\text {N}_2\) ${\text{N}}_2$ nanoclusters have a two shell structure, an outer shell which contains high concentration of stabilized N atoms and an interior shell with lower concentrations of N atoms. In this paper, we have studied the dependence of the shell structure of the \(\text {N}_2\) ${\text{N}}_2$ nanoclusters which compose the IHCs by varying the ratio of nitrogen to helium in the prepared gas mixture from 0.06 to 1%. The highest local concentration of N atoms in nanoclusters (1.2 \(\cdot\) $·$ \(\text {10}^{21}\) ${\text{10}}^{21}$ \(\text {cm}^{-3}\) ${\text{cm}}^{-3}$ ) was observed in the sample prepared from the gas mixture containing the lowest nitrogen admixture (0.06%). Additionally, the evolution of nanocluster structure was studied as the samples were drained of liquid helium (T \(\le\) $\le$ 3.5 K) and warmed beyond the point of explosive recombination (3.5 K \(\le\) $\le$ T \(\le\) $\le$ 6.5 K).