Alkali-metal-halogen charge-exchange collisions

An approximate quasiclassical treatment is presented for calculating the cross sections for charge transfer from a neutral alkali-metal atom colliding with a halogen atom (chlorine or fluorine). The electron is treated by the time-dependent perturbation in the two-state approximation. The two states are the ground (or the first-excited) state of alkali-metal atom and the ground state of the halogen negative ion. Charge-transfer cross sections are calculated as a function of relative velocity ($v$) of collision between $v=0.01\mathrm{} \mathrm{and} 5$ a.u. Qualitative features of these cross sections are compared with an earlier work on alkali-metal-oxygen collisions. An asymptotic formula at low velocities of collision $v\to 0$ is obtained, which compares with the earlier formula obtained by Bates. At higher velocities cross sections are found to vary as $\frac{1}{v^2}$, as in the Born approximation.