Study of Nanoclusters Containing High Concentrations of Stabilized Atoms by Optical and Electron Spin Resonance Methods

Abstract

Impurity-helium condensates (IHCs) are a new class of non-crystalline materials formed by injecting a gas mixture consisting of helium gas and an impurity gas into superfluid helium. We studied dynamics of thermoluminescence during destruction of porous structures formed by nanoclusters of nitrogen molecules containing high concentrations of stabilized nitrogen atoms. Porous structures were formed in bulk superfluid helium by injection of the products of discharges in nitrogen-helium gas mixtures through the liquid helium surface. Fast recombination of nitrogen atoms during warming-up led to explosive destruction of the porous structures accompanied by bright ashes.

We also investigated thermoluminescence of ensembles of molecular nitrogen nanoclusters, containing stabilized nitrogen atoms, immersed in liquid helium. We obtained experimental evidence for quantum vortex induced chemical reactions for nitrogen atoms in HeII leading to the appearance of luminescence. Thermoluminescence was also observed in HeI due to the process of nanocluster association resulting in thermal explosions of a small fraction of nanoclusters. Impurity-helium condensates created by injection of nitrogen atoms and molecules as well as rare gas (RG) atoms (Ne, Ar and Kr) into superfluid 4He also have been studied via electron spin resonance (ESR) techniques and optical spectroscopy. Measurements of the ground-state spectroscopic parameters of nitrogen atoms show that the nanoclusters have a shell structure. N and O atoms reside in solid molecular layers of N2. These layers form on the surfaces of RG (Ar or Kr) nanoclusters. We studied the dynamics of thermoluminescence spectra emitted during the warming of porous N-N2-RG-He samples inside the superfluid helium. Using this experimental approach, it is possible to study chemical reactions of heavy atoms and molecules at very low temperatures where normally diffusion and quantum tunneling in solid matrices not possible.