The Production of Hot Oxygen at the Exobases of the Terrestrial Planets

Hot oxygen is produced in mainly in dissociative recombination of O ₂ ⁺ at the exobases of the terrestrial planets. Models of the vibrational distribution of O ₂ ⁺ in the ionospheres of Earth, Venus and Mars are combined with the calculations of Guberman [1987,1988] of the rate coefficients for the channels producing excited states of atomic oxygen in dissociative recombination of O ₂ ⁺ ( v ) and measurements of the total rate of dissociative recombination to give the fractional yields of the channels O ( ³ P ) + O ( ³ P ), O ( ¹ D ) + O ( ³ P ), O ( ¹ S ) + O ( ³ P ), O ( ¹ S ) + O ( ¹ D ), and O ( ¹ D ) + O ( ¹ D ). These calculations also produce a distribution of the velocities of O atoms released at the exobases. The major source of error in the calculation involves the yield of the channel in which two ground state oxygen atoms are produced, which is computed as the difference between the sum of the rates of excited state production and the total dissociative recombination rate. Implications for the hot oxygen coronas of the Earth and planets are discussed.