Ionic recombination of atomic and molecular ions in flowing afterglow plasmas

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Abstract
Measurements are reported of the decay of ionisation in positive-ion/negative-ion flowing afterglow plasmas. When one or both of the ion species is molecular, conditions of pressure and ionisation density can be readily established under which mutual neutralisation (ionic recombination) dominates over ambipolar diffusion and hence the recombination coefficient alpha i can readily be determined. When both ionic species are atomic the recombination rate is so slow that ambipolar diffusion is seen to dominate over ionic recombination under the conditions of the experiment, and it has only been possible to determine upper limits for alpha i.