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 $2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}{\mathrm{cm}}^{2}(\frac{Q}{e{{a}_{0}}^{2}})(1 \mathrm{eV}/{E}_{i})\ensuremath{\eta}(J)$, where ${E}_{i}$ is the incident electron energy and $\frac{1}{4}<\ensuremath{\eta}(J)<\frac{2}{3}$ 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.