High-speed correction factor to the O⁺-O resonance charge exchange collision frequency

Abstract. The high-speed correction factor to the O⁺-O collision frequency, resulting from drift velocities between ions and neutrals, is calculated by solving the integral expression in this factor both numerically and analytically. Although the analytic solution is valid for either small or large drift velocities between ions and neutrals, for temperatures of interest and all drift velocities considered, agreement is found between analytic and detailed numerical integration results within less than 1% error. Let T_r designate the average of the ion and neutral temperatures in K, and u=v_d/α, where v_d is the relative drift velocity in cm s^-1, and α=4.56×10³√T_r cm s^-1 is the thermal velocity of the O⁺-O system. Then, as u ranges from 0 to 2, the correction factor multiplying the collision frequency increases monotonically from 1 to about 1.5. An interesting result emerging from this calculation is that the correction factor for temperatures of aeronomical interest is to a good approximation independent of the temperature, depending only on the scaled velocity u.