Townsend Ionization Coefficient for Hydrogen and Deuterium

The Townsend ionization coefficient $\frac{\alpha }{p_0}$ ${(\mathrm{c}\mathrm{m}\times \mathrm{mm}\mathrm{Hg}\mathrm{at}0\mathrm{}\mathrm{°}\mathrm{C})}^{-1\mathrm{}}$ for hydrogen and deuterium has been measured as a function of $\frac{E}{p_0}$ (volts/cm×mm Hg at 0°C) over an extended range. The results for ${\mathrm{H}}_2$ have been compared critically with those of previous workers. They agree well with several recent redeterminations over limited ranges of $\frac{E}{p_0}$, but not with several earlier extensive investigations. The composite results for ${\mathrm{H}}_2$ ($15<\mathrm{}\frac{E}{p_0}<1000\mathrm{}$), and present data for ${\mathrm{D}}_2$ ($18<\mathrm{}\frac{E}{p_0}<600\mathrm{}$), are presented in graphical and tabular form. The difference between the two coefficients is discussed in terms of the molecular properties of the two gases. It appears that the difference in energy loss by recoil on electron impact is insufficient to explain the observed effect.