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\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ and 15\ifmmode\pm\else\textpm\fi{}2 meV. The cross sections at $\ensuremath{\epsilon}<0.010$ 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 ${\ensuremath{\theta}}_{n,T}={(\frac{\ensuremath{\partial}log(\ensuremath{\mu}n)}{\ensuremath{\partial}logT})}_{n,T}$ near the vapor-liquid coexistence curve increases from -0.6 at the low-density limit and 80 K to zero at $\frac{n}{{n}_{c}}\ensuremath{\ge}0.5$ and $\frac{T}{{T}_{c}}>0.97$. While $\frac{n}{{n}_{c}}$ increases from 0.5 to 1.0 along the coexistence curve, the density-normalized mobility $\ensuremath{\mu}n$ decreases from 14 to 1.0 (${10}^{22}$ molecule/cm Vs) and the electric-field effect $\frac{d\ensuremath{\mu}}{\mathrm{dE}}$ changes sign from negative to positive. This behavior at high densities is attributed to electron capture, ${e}^{\ensuremath{-}}+{\mathrm{N}}_{2}\ensuremath{\rightleftharpoons}{\mathrm{N}}_{2}{\ensuremath{\rightleftharpoons}}^{\ensuremath{-}\mathrm{N}2}{({\mathrm{N}}_{2})}_{2}{\ensuremath{\rightleftharpoons}}^{\ensuremath{-}\mathrm{N}2}$ and so on. The capture coefficient ${\ensuremath{\nu}}_{a}$ decreases with increasing electron energy.