Curved Trajectory Effect on Charge‐Exchange Collision at Ionospheric Temperatures

Abstract

Ions collide with neutral particles in Earth's ionosphere. This ion-neutral collision is represented by the collision cross section or frequency. Accordingly, an accurate model of the cross section is necessary to study the ionosphere.There are two types of ion-neutral collision (e.g., Banks & Kockarts, 1973). One is electric-polarization collision, which occurs in all ion-neutral pairs because a neutral particle is polarized by an ion. The corresponding cross section is expressed by a classic theoretical functional form of the polarization collision.The other is charge-exchange collision, which effectively occurs between an ion and its parent atom, such as O + and O, because the energy state is the same before and after the electron transfer. The corresponding cross section has been expressed by a classic theoretical functional form of the charge-exchange collision. This form is appropriate at high temperatures, but its validity has been less clear at ionospheric temperatures, where the values are extrapolated.For the parental particle pair, the polarization collision dominates at low temperatures (i.e., low kinetic energy), whereas the charge-exchange collision dominates at high temperatures (Figure 1). The total cross section for momentum transfer is not the sum of the polarization and charge-exchange components (Banks & Kockarts, 1973, p. 211). Instead, the total is equal to the dominant component at most temperatures. The total cross section is enhanced, that is, higher than the dominant component, only near the classic transition temperature, which corresponds to the intersection of the polarization and charge-exchange components in Figure 1.