The recombination of H3+ and H5+ ions with electrons in hydrogen plasma: dependence on temperature and on pressure of H2

The recombination of H3+ and H5+ ions with electrons has been studied in a low-temperature, high-pressure flowing afterglow in a mixture of He-Ar-H2. At high H2 number densities and lower temperatures, H5+ ions are formed and the electron decay is controlled by their recombination with electrons (rate coefficient alpha(H5+)). At lower H2 number densities, H3+ ions dominate the plasma and the decay is controlled by these ions (rate coefficient alpha(H3+)). In the intermediate pressure regime the decay of the afterglow plasma depends on the ratio R=[H5+]/[H3+]=[H2]KC(T) and both rate coefficients. In the experiment the overall effective recombination rate coefficient, alphaeff, as a function of the H2 number density was measured. Recombination coefficients alpha(H3+) and alpha(H5+) and the equilibrium constant, KC(T), were determined at several temperatures. The observed pressure and temperature dependences are in good agreement with thermodynamical data