Electron motion in high-pressure polar gases: NH3

Drift velocities w for slow electrons in ${\mathrm{NH}}_3$ vapor have been measured and are reported as a function of the density‐reduced electric field E/N ${\text{(⩽24×10}}^{\text{−17}}\hspace{0.17em}\mathrm{V}\hspace{0.17em}{\mathrm{cm}}^2\mathrm{),}$ density N ${\text{(2.43–292×10}}^{18}\hspace{0.17em}\mathrm{molecule}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}\mathrm{),}$ and temperature T $\text{(300–650\hspace{0.17em}}\mathrm{K}\mathrm{).}$ The w decreases with increasing N considerably and this decrease varies with T; for a fixed N it is higher the lower the T. Use is made of the T‐ and N‐dependence of w to assess the role of the various processes which delay the electron drift. The density range above ${\text{∼2.5×10}}^{19}\hspace{0.17em}\mathrm{molecules}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}$ seems to represent the transition from the free (or quasifree) to the localized (anionic) electron state. The number density $N_L$ at which complete electron localization occurs, has been estimated at various T. At $\text{T=300\hspace{0.17em}}\mathrm{K},$ $N_L{\text{≃3.3×10}}^{20}\hspace{0.17em}\mathrm{molecule}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}$ or $\text{∼0.01\hspace{0.17em}}\mathrm{g}\hspace{0.17em}{\mathrm{cm}}^3.$ Estimates have also been made of the binding energy of the electron to the trapping species (possibly ${\mathrm{NH}}_3$ clusters) which, depending on T, range from 0.11 to 0.15 eV.