We report the results of a spectroscopic investigation concerning the time evolution of level populations of atomic hydrogen in the afterglow following a pulsed high-voltage hollow- cathode discharge in noble gases under various discharge conditions (peak voltage across the tube of 4 - 20 kV peak current of 50 - 150 A, halfwidth duration of the current pulse of 30 - 100 ns, repetition rate of 30 Hz, and 1 - 15 torr noble as pressure). A long afterglow duration (more than 100 microsecond(s) ) of the Balmer lines has been observed in helium and neon, accompanied by a population inversion between the n equals 3 and n equals 4, 5, 6 levels of the hydrogen atom. We assume that this behavior of level populations of atomic hydrogen is primarily due to the Penning ionization of hydrogen molecules by collisions with noble gas metastables and by metastable-metastable ionization, followed by selective production of excited atomic hydrogen by dissociative recombination of the molecular hydrogen ion. A simple theoretical model based on these assumptions agrees with the observed shape and size of temporal profiles of hydrogen impurity level populations in helium and neon afterglow.
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