Electron motion in high-pressure polar gases: NH₃

Drift velocities w for slow electrons in NH₃ vapor have been measured and are reported as a function of the density-reduced electric field E/N (≤24×10^-17 V cm²), density N (2.43-292×10¹⁸ molecule cm^-3), and temperature T (300-650 K). 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 ∼2.5×10¹⁹ molecules cm^-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 T=300 K, N_L≃3.3×10²⁰ molecule cm^-3 or ∼0.01 g cm³. Estimates have also been made of the binding energy of the electron to the trapping species (possibly NH ₃ clusters) which, depending on T, range from 0.11 to 0.15 eV.