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

Abstract

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; α(Te)=2.4×10−7(300/Te)0.70±0.01 cm3 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.