Ar⁺ in the Terrestrial Atmosphere

Ar ⁺ in the terrestrial ionosphere is produced by photoionization and electron impact ionization and by the reaction

N ₂ ⁺ (v > 1) + Ar → Ar ⁺ + N ₂ (1)

The rate coefficient for (1) has been measured by a number of workers and has been found to approach gas kinetic rates. For v=0, the reaction proceeds in the reverse direction. For this reason, the Ar ⁺ densities provide a sensitive measure of the extent of vibrational excitation of N ₂ ⁺ in the terrestrial ionosphere. Model calculations show that at 200 km, half of the source of Ar ⁺ is due to (1). The total density of Ar ⁺ is on the order of 10cm ^-3 near 200 km.