Optical Emissions from Ensembles of Nanoclusters with High Concentrations of Stabilized Nitrogen Atoms
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Ensembles of nanoclusters are formed in bulk HeII by the injection of products of a radiofrequency discharge in impurity-helium gas mixtures into bulk superfluid ^4He (HeII). The ensembles of nanoclusters contain high concentrations of stabilized nitrogen atoms residing mostly on the surfaces of rare gas or nitrogen nanoclusters. These samples are characterized by a high energy density which allows the study of energy release processes in chemical reactions initiated by warming ensembles of nanoclusters. Optical spectra in the ultra-violet, visible, and near-infrared ranges were recorded during the destruction of these ensembles of nanoclusters, accompanied by a rapid release of chemical energy stored in the samples. Rare gases such as neon, argon, and krypton were used to study the effects of changing the relative concentrations of nitrogen in rare gases used for sample preparation on thermoluminescence spectra during destruction of nitrogen-rare gas-helium samples. Spectra obtained during the bright flashes of the final destruction of the samples contain M- and β-bands of NO molecules the intensities of which depend on concentration of molecular nitrogen in the gas mixture as well as on the type of rare gas present in the gas mixture. During the destructions of samples containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms, the known bands of atomic nitrogen and oxygen, and bands of molecular nitrogen, oxygen, and NO were observed as well as several other interesting features including a broad band near ʎ ~ 360 nm, which has been identified as an emission corresponding to the 2Avg →1Avg transition of Nv4(Dv2h) polymeric nitrogen. Also the sharp lines at ʎ = 336 nm, 473 nm, and 1170 nm were observed, which were assigned to the emission of the ND radicals formed due to recombinations of nitrogen atoms in excited metastable states and deuterium atoms in the ground state during the destruction of ensembles of molecular nitrogen nanoclusters. The influence of rotation speed of a beaker containing HeII on the intensity of luminescence of collections of nanoclusters immersed in HeII was also studied. Luminescence was found to increase with the concentration of molecular nitrogen in the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. The intensity of α-group emission of nitrogen atoms (^2D → ^4S transition) in nanoclusters also increased with the rotational speed of the beaker. We suggest that this effect is connected to the processes of recombination of nitrogen atoms residing on the surfaces of nanoclusters after their trapping into quantum vortices in HeII. Increasing the rotation speed of the beaker results in the increasing density of quantum vortices in HeII. The probability for nanoclusters to become trapped in the vortex cores increases with the vortex density. Inside the vortex cores, the collision rate of nanoclusters increases substantially, leading to more efficient recombination of nitrogen atoms stabilized on the surfaces of nanoclusters and, therefore to more intense atomic nitrogen luminescence.
Electron Spin Resonance Spectroscopy
High Energy Density Materials
McColgan, Patrick Thomas (2018). Optical Emissions from Ensembles of Nanoclusters with High Concentrations of Stabilized Nitrogen Atoms. Doctoral dissertation, Texas A & M University. Available electronically from