Quantum vortices and thermally induced luminescence of nitrogen nanoclusters immersed in liquid helium

Abstract

We performed investigations of ensembles of molecular nitrogen nanoclusters, containing stabilized nitrogen atoms, immersed in liquid helium by electron spin resonance and optical spectroscopy. We observed thermoluminescence of nitrogen atoms and molecules via increasing temperature from 1.25 to 4.4 K. Two thermoluminescence maxima were observed, one in superfluid helium (HeII) at $T\ensuremath{\sim}1.9$ K and another in normal helium (HeI) at $T\ensuremath{\sim}3.2\phantom{\rule{4pt}{0ex}}\mathrm{K}$. We explain appearance of luminescence in HeII by chemical reactions of nitrogen atoms on surfaces of nanoclusters which might be initiated by quantum vortices. Thermoluminescence in HeI occurs due to the process of nanocluster association resulting in thermal explosions of a small fraction of nanoclusters. This research might open new possibilities for studying a broad range of chemical reactions initiated by quantum vortices in HeII.