Dissociative recombination and excitation of O2+: Cross sections, product yields and implications for studies of the ionospheric airglows

We present experimental data on the dissociative recombination (DR) and the dissociative excitation (DE) of O₂⁺ in its electronic and vibrational ground state using a heavy ion storage ring. The absolute DR cross section has been determined over an electron collision energy range from 1 meV to 3 eV. The thermal DR rate coefficient is derived; a(T_e) = 2.4×10^–7(300/T_e)^0.70±0.01cm³ s^–1, for T>200 K. The threshold for DE was observed near its energetic threshold of 6.7 eV. The DE cross section curve has a maximum of 3×10^–16 cm² near 15 eV. We have determined the branching fractions to the different dissociation limits and present atomic quantum yields for the DR process between 0 to 300 meV collision energy. The quantum yield of O(¹D) is found to be 1.17±0.05, largely independent of the electron energy. Arguments are presented that the branching fraction to O(³P) + O(¹S) is negligible. The branching fraction to the O(¹S) + O(¹D) is smaller than 0.06 and varies strongly as a function of collision energy. The O(¹S) quantum yield is a strong function of electron temperature. Hence, the relative strength of the green, O(¹S), and the red, O(¹D), airglows may be used as a measure of the electron temperature of the upper atmosphere. A qualitative explanation is given of the consequences of nonadiabatic interactions in the dissociation step of the DR process.