Rotational Excitation of Molecular Ions by Slow Electrons

Abstract

The cross section for the excitation of rotation of a molecular ion by low-energy electrons has been calculated using first-order perturbation theory and approximate Coulomb wave functions. For ions with vanishing electric dipole moment, quadrupole moment $Q$, and rotational quantum number $J$, the cross section is found to be $2.0\times {10}^{-15\mathrm{}}{\mathrm{cm}}^2\left(\frac{Q}{e{a_0}^2}\right)(1\mathrm{} \mathrm{eV}/E_i)\eta \mathrm{}\left(J\right)\mathrm{}$, where $E_i$ is the incident electron energy and $\frac{1}{4}<\eta \mathrm{}\left(J\right)<\frac{2}{3}$ for all $J$. The rate-of-energy loss to molecular ions arising from these inelastic collisions is found to be about 10% of the loss from elastic Coulomb collisions, independent of energy. This mechanism, thus, will result in a slight increase in the energy-transfer collision frequency under conditions where molecular ions are present.