Regular Article

Monitoring the removal of excited particles in He/Ar/H₂ low temperature afterglow plasma at 80–300 K^*

¹ Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University in Prague, 18000 Prague, Czech Republic
² JILA, University of Colorado and National Institute of Standards and Technology, 80309-0440 Boulder, Colorado, USA

^a e-mail: juraj.glosik@mff.cuni.cz

Received: 30 November 2015
Revised: 14 January 2016
Accepted: 20 January 2016
Published online: 8 August 2016

Abstract

Stationary afterglow (SA) experiments with cavity ring down absorption spectrometer (cw-CRDS) have been used to study recombination of H₃⁺ ions with electrons. To characterize the plasma during the afterglow we monitored the time evolution of density of He₂ excited dimers (a³Ʃ_u⁺) in plasmas in pure helium and in helium with small admixture of Ar and H₂. By monitoring the plasma decay and its dependence on [H₂] and [Ar] in the afterglow in pure He and in He/Ar/H₂ mixture we estimated the rate of plasma thermalization in the temperature range of 80–300 K. The inferred deexcitation rate coefficients for reaction of helium metastable atoms with H₂ were (0.9 ± 0.3) × 10⁻¹⁰ cm³ s⁻¹, (1.9 ± 0.2) × 10⁻¹⁰ cm³ s⁻¹ and (2.7 ± 0.2) × 10⁻¹⁰ cm³ s⁻¹ at 80 K, 140 K and 300 K, respectively. The effective recombination rate coefficients for H₃⁺ were evaluated from the decay of the electron number density. We propose the lower estimate for the saturation of the effective recombination rate coefficient in H₃⁺ and D₃⁺ dominated plasma.