The motion of oxygen ions in oxygen

Abstract

The drift velocities of positive and negative ions produced in a glow discharge in oxygen were measured within the range 5 < E/p 0 < 100 v cm-1 torr-1 (E is the electric field and p 0 the gas pressure reduced to 0 °c) for values of p 0 in the range 7·71 to 0·83 torr. The results for negative ions were in agreement with previous data on ion species generally believed to be O3 - and O2 -. In the case of positive ions, on the other hand, the results were quite different from those obtained by previous investigators in that two species of ions were observed. For E/p 0 < 15 v cm-1 torr-1 only the faster species was present, and for E/p 0 > 28 v cm-1 torr-1 only the slower species, but in the intermediate region the results indicated that the ion species interacted with the gas molecules, the dominant species being dependent critically on the experimental conditions. Measurements were also made of the ratio D/K (D the diffusion coefficient and K the mobility) for the positive ion species. The drift and diffusion data for the positive ions were used to show that the binding energy of the faster ion species was 0·45 ev. Since this value is in close agreement with that of 0·42 ev previously determined for the binding energy of O4 +, the present results are consistent with the identification of the faster species as O4 + and the slower species as O2 +, and with the view that for 19 < E/p 0 < 25 v cm-1 torr-1 the reaction between the ions and the gas molecules was of the form O4 + &rlarr2; O2 + + O2. The drift and diffusion data for the slower species were also used to obtain information about the collision cross section of these ions.