The Mobility of Electrons in Pure Nitrogen

Abstract

Mobility of electrons in pure nitrogen was determined, using the Rutherford alternating potential method, for pressures ranging from $75 \mathrm{to} 600$ mm., for frequencies ranging from $7,000 \mathrm{to} 150,000$ cycles (obtained from an audion oscillating circuit), and with electric fields of from 10 to 100 volts/cm. Reduced to atmospheric pressure the mobility found is of the order of 10,000\ifmmode\cdot\else\textperiodcentered\fi{} cm. sec.,/many times the highest value previously obtained, and it was observed to vary with pressure and electric field according to the equation $K=\frac{571,000}{(21+760 \frac{V}{\mathrm{pd}})}$, where $\frac{V}{d}$ is in volts/cm. and $p$ in mm. of Hg. A discussion of the possible sources of error shows that none can be responsible for this variation with $\frac{V}{\mathrm{pd}}$, and the form of the mobility curves confirms this variation. A theoretical interpretation of these results on the basis of the Townsend equation for electron mobility leads to the conclusions: that if the Townsend theory is correct (1) either the energy lost at each impact of an electron with a nitrogen molecule or the mean free path must be a function of $\frac{V}{\mathrm{pd}}$, and (2) in either case the mean free path for velocities of the normal agitation must be about 22 times the mean free path of the gas molecules instead of $4 \sqrt{2}$ times, as given by the kinetic theory.