A method is described for measuring cross sections for ion charge exchange at mean ion energies corresponding to gas temperatures of the order of 300 K.
The measurements are made in afterglows following pulsed radio-frequency gas discharges, using a mass spectrometer to identify the ions present, and to observe their relative rates of change of population.
The reaction cross section for the process O++O2->O2++O has been deduced from the measured population decay rate of the O+ ion, at gas temperatures from 200°K to 300°K.
The apparent variation of the cross section with gas temperature is not considered to indicate a systematic temperature dependence.
The cross section was found to be 3.2 ± 0.5 × 10-16 cm2, corresponding to a rate coefficient of 2.5 ± 0.4 × 10-11 cm3 sec-1, for the process.
The relevance of this result to upper ionospheric studies is briefly discussed.