Collision between ions and neutral particles is an essential characteristic of Earth’s ionosphere. This ion-neutral collision is usually caused by the polarization of neutral particles. This collision can also be caused by charge exchange, if the particle pair is parental, such as atomic oxygen and its ion. The total collision frequency is not the sum of the polarization and charge-exchange components, but is essentially equal to the dominant component. The total is enhanced only around the classic transition temperature, which is near the ionospheric temperature range (typically 200-2000 K). However, the magnitude of this enhancement has differed among previous studies; the maximum enhancement has been reported as 41% and 11% without physical explanation. In the present study, the contribution of the polarization force to the charge-exchange collision is expressed as a simple curved particle trajectory effect. As a result, the maximum enhancement is found to be 22%. It is discussed that the enhancement has been neglected in classic models partly due to confusion with the glancing particle contribution, which adds 10.5% to the polarization component. The enhancement has been neglected presumably also because there has been no functional form to express it. Such an expression is derived in this study.

Molecular oxygen collides with its first positive ion in the earth’s ionosphere. The collision frequency of this particle pair is used to calculate the electric conductivity. However, for this parental pair there are two collision types, resonant and nonresonant, and the selection of the collision type has been different among previous studies in calculation of conductivity. In the present study we clarify that the nonresonant collision is essential for this pair because relevant temperatures are low. That is, the peak of the ionospheric conductivity is located at altitudes between 100 and 130 km, where the temperatures of ions and neutral particles are usually lower than 600 K, for which nonresonant collision is dominant. The collision frequency would be underestimated by 30% if the resonant collision was assumed at 110-km altitude (where the temperature is 240 K). The impact of this difference on the conductivity is estimated to be small (3%), primarily because molecular nitrogen is much more abundant than molecular oxygen. Although we have confirmed that the nonresonant collision is essential, we also include the resonant type, primarily in case of possible elevated temperature events. A set of ion–neutral collision frequency coefficients for calculating the conductivity is summarized, including other particle pairs, in the Appendices. Small corrections to the classical coefficients are made.

The Earth’s F region ionosphere is dominated by the collision between atomic oxygen and its first positive ion. An accurate corresponding collision frequency model is necessary to understand the ionosphere. However, the widely used classic Banks theoretical model typically provides a collision frequency that is 30% lower than the expectation from ionospheric observations. Accordingly, the classic collision frequency is often adjusted by multiplying it by a constant known as the Burnside factor. This correction-factor model adopted the classic model as its basis due to a misunderstanding that the classic model was based on a laboratory experiment; that is, the correction factor was originally meant to compensate for laboratory contamination. In this study, we construct a collision frequency model based on the laboratory experiment. We find that the resultant laboratory-based model is consistent with ionospheric observations. In this construction, we have determined that the impact of laboratory contamination is small (7%) and is mostly canceled by a misinterpretation regarding the conventional definitions of energy. Thus, the 30% difference is mainly caused by a theoretical error in the classic model itself. This error is energy-dependent and corrected by the later wide-energy theoretical model. Thus, the classic model cannot be corrected by a constant and should be replaced by the later model.