The recombination of H+3 and H+5 ions with electrons in hydrogen plasma:: dependence on temperature and on pressure of H2

The recombination of H-3(+) and H-5(+) ions with electrons has been studied in a low-temperature, high-pressure flowing afterglow in a mixture of He-Ar-H-2. At high H-2 number densities and lower temperatures, H' ions are formed and the electron decay is controlled by their recombination with electrons (rate coefficient alpha (H-5(+))). At lower H-2 number densities, H' ions dominate the plasma and the decay is controlled by these ions (rate coefficient alpha (H-3(+))). In the intermediate pressure regime the decay of the afterglow plasma depends on the ratio R = [H-5(+)]/[H-3(+)] = [H-2]K-C(T) and both rate coefficients. In the experiment the overall effective recombination rate coefficient, alpha(eff), as a function of the H-2 number density was measured. Recombination coefficients alpha (H-3(+)) and alpha (H-5(+)) and the equilibrium constant, K-C(T), were determined at several temperatures. The observed pressure and temperature dependences are in good agreement with thermodynamical data.