Ion-ion recombination in mixtures of methane and sulphur hexafluoride

Abstract

The authors have measured the recombination rate for positive and negative ions in sulphur hexafluoride and in mixtures of methane and sulphur hexafluoride in an electron beam sustained discharge. Measurements were made as a function of gas composition, gas pressure in the range 100 to 600 Torr, and reduced electric field strength in the range 12 to 150 Td. When plotted as a function of an effective ion temperature, defined by the drift velocities of the ions in the applied electric field, the rates in each of the gas mixtures follow the same Teff-1.6 power law. From comparisons with theories appropriate to the recombination of positive ions with electrons it is suggested that the index of the power law might indicate that the recombination process follows an indirect path, with the approaching ions being initially trapped in stable orbits before final stabilisation of the collision.