Ion neutralisation rates in gaseous ammonia

Abstract

Ion-ion and electron-ion recombination have been studied in ammonia by several different experiemental techniques. With the addition of nitrous oxide, stable clustered negative ions are formed and the homogeneous ion-ion combination coefficient α was determined from steady state ion concentrations and from their decay with time for NH 3 pressures in the range 35–1200 torr (4.7–160.0 kPa) at 298 K. Both methods gave the same results. The maximum α value (1.57 × 10 -6 cm 3 s -1) was at 350 torr (46.7 kPa), while at 35 and 1200 torr (4.7 and 160.0 kPa), the values were 0.75 and 1.16 × 10 -6 cm 3 s -1, respectively. The average ion mobilities over this pressure range are also reported. The homogeneous electron-ion combination coefficients in pure ammonia at 298 K were much larger and varied from 6.7 × 10 -5 cm 3 s -1 at 350 torr (46.7 kPa) to 5.6 × 10 -5 cm 3 s -1 at 1200 torr (160.0 kPa). The reaction showed a negative temperature coefficient at both extremes of this pressure range. The magnitudes of ion and electron loss by wall diffusion and the electrical fields due to space charges near the wall were computed and found to be small for the above pressure regime at typical gamma ray dose rates.