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Rate coefficients for nuclear spin state-specific recombination of H3+ ions with thermal electrons were measured using FALP and SA techniques at temperatures 77–300 K. For this purpose H2 gas with both thermal and enriched population of the para nuclear spin configuration was used. Measurements have shown that at 77 K para-H3+ exhibits five times higher binary recombination rate coefficient than ortho-H3+: (1.5 ± 0.4) × 10−7 vs. (3 ± 2) × 10−8 cm3s−1.

Stationary afterglow (SA) experiments with cavity ring down absorption spectrometer (cw-CRDS) have been used to study recombination of H+3 ions with electrons. To characterize the plasma during the afterglow we monitored the time evolution of density of He2 excited dimers (a³Σ+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 H+3 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 H+3 and D+3 dominated plasma. [ABSTRACT FROM AUTHOR]