Temperature, density, and electric-field effects on electron mobility in nitrogen vapor

Abstract

A detailed study of the effect of temperature on electron mobility in low-density nitrogen gas has revealed a Ramsauer-Townsend minimum in the scattering cross section at 1.7×${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ and 15±2 meV. The cross sections at $\epsilon <0.010\mathrm{}$ eV are much larger than those previously reported. Energy gained by the electrons from the field is imparted to the molecules mainly through inelastic collisions, down to mean energies of a few meV. With increasing gas density the temperature coefficient ${\theta }_{n,T}={\left(\frac{\partial log\left(\mu n\right)}{\partial logT}\right)}_{n,T}$ near the vapor-liquid coexistence curve increases from -0.6 at the low-density limit and 80 K to zero at $\frac{n}{n_c}\ge 0.5$ and $\frac{T}{T_c}>0.97\mathrm{}$. While $\frac{n}{n_c}$ increases from 0.5 to 1.0 along the coexistence curve, the density-normalized mobility $\mu n$ decreases from 14 to 1.0 (${10}^{22}$ molecule/cm Vs) and the electric-field effect $\frac{d\mu }{\mathrm{dE}}$ changes sign from negative to positive. This behavior at high densities is attributed to electron capture, $e^{-}+{\mathrm{N}}_2\rightleftharpoons {\mathrm{N}}_2{\rightleftharpoons }^{-\mathrm{N}2}{\left({\mathrm{N}}_2\right)}_2{\rightleftharpoons }^{-\mathrm{N}2}$ and so on. The capture coefficient ${\nu }_a$ decreases with increasing electron energy.