The recombination of D+3 and D+5 ions with electrons in deuterium containing plasma

Abstract

The recombination of D+3 and D+5 ions with electrons in a He–Ar–D2 flowing afterglow plasma is reported. Low temperature (T = 130–300 K) and high pressure of the He buffer gas (900–1200 Pa) was used to enhance the formation of D+5 ions in the afterglow plasma. The deuterium partial number density was varied over a large range ([D2] = 1 × 1012–3 × 1015 cm−3) to study its influence on plasma decay. At low [D2], D+3 ions dominate in the afterglow and the plasma decay is controlled by the recombination of D+3 ions (rate coefficient α3). At high [D2] and lower temperatures, D+5 ions are effectively formed and the plasma decay is controlled by the recombination of D+5 ions (α5). In the intermediate region, the rate of recombination is given by the partial densities of both ions, D+3 and D+5. These partial densities are influenced by conditions in the plasma and they are controlled by ion–molecule reactions (D+3 + D2 ↔ D+5). If the ion–molecule reactions are fast in comparison with the recombination processes the plasma decay can be characterized by the equilibrium constant KC and by recombination rate coefficients α3 and α5. By monitoring of the plasma decay, all three constants α3 (190 K) = (1.4 ± 0.5) × 10−7 cm3 s−1, α5 (190 K) = (3 ± 1) × 10−6 cm3 s−1 and KC (190 K) = (3.8 ± 2.0) × 10−16 cm3 are determined.