The Recombination of Ions in Pure Oxygen as a Function of Pressure and Temperature

All previous investigations of the coefficient of recombination in pure gases have employed the older technique which did not allow the use of an outgassed chamber and made no corrections for initial recombination, diffusion, etc. This work was undertaken in pure oxygen in order to compare the results with existing theories. Aside from the initial drop in the curves of the recombination coefficient plotted against time due to preferential and initial recombination, the value of the coefficient of recombination in oxygen was found to be constant at a given pressure over extended intervals of time. It was, accordingly, possible to obtain a definite and probably correct value for the coefficient of recombination in pure oxygen at 76 cm pressure and 25°C. This value is $\alpha =(2.08\mathrm{}\pm 0.05)\times {10}^{-6\mathrm{}}$. Comparison of the variation with pressure in the range 10 cm to 76 cm pressure was approximately in good agreement with the theory of J. J. Thomson assuming the ion to have a mass of $M=64\mathrm{}$ and a mean free path of that given by mobility measurements. The temperature variation between the limits of -78°C to +105°C verified the Thomson equation quite accurately using the same data concerning the ion. At the lowest temperature a deviation was observed, indicating a possible increase of ionic mass to 96. While these results are a good confirmation of the Thomson theory they cannot be reconciled with the Langevin theory, although the Langevin theory probably holds beyond 10 atmospheres. Loeb has indicated the character of the transition between the two theories. The outstanding difficulty introduced by the change in the coefficient with time, due presumably to initial recombination, which is impossible of analysis in the less pure gases of the previous workers, is now somewhat more amenable to treatment. It is shown that if one includes the retarded diffusion of the ions created within ten times the radius of the sphere of active attraction, the time intervals involved in the x-ray flash periods, and the gradual formation of ions of mass $M=64\mathrm{}$ from the initially ionized particles which may be accelerated by x-ray irradiation, the rough theory of initial recombination given by Loeb will account for the behavior.