Electron collisions with highly polar molecules: Comparison of model, static, and static-exchange calculations for alkali-metal halides

Abstract

Calculations of cross sections for (vibrationally and electronically) elastic collisions of electrons with several alkali-metal halides were performed for energies in the range of 0.13 to 20.0 eV. The applicability of the adiabatic (fixed-nuclei) approximation for strongly polar systems is investigated by model calculations on CsF, KI, and LiF. We demonstrate that integrated, momentum transfer, and differential cross sections for polar systems can be reliably generated entirely within the body-frame, adiabatic approximation. We also suggest resolutions of several discrepancies between the results of earlier calculations and between these results and measurements. Close-coupling calculations, based on the adiabatic approximation and an alternative form of the frame transformation, were performed for electron-LiF collisions using the full static and static model-exchange surface. Reasonable agreement was found with measured differential cross sections at 5.44 and 20.0 eV. Shape resonances in the $\Sigma$ and $\Pi$ body-frame symmetries, centered near 1.8 and 1.5 eV, respectively, were observed. Similar features appeared in static-exchange calculation for NaF and NaCl. We also compare the results of the static and static-exchange calculations with the results of calculations using simpler model potentials and other approaches to the collision problem.