Elastic scattering of very slow electrons by molecules

The modified effective-range theory, which has enjoyed great success in its application to electron-atom scattering, is hereby extended to electron scattering from molecules. An analytic expression for the diffusion cross section for molecules in any rotational state is obtained. It is utilized to analyze the detailed results of recent swarm experiments on ${\mathrm{H}}_2$, and to comment on the less-detailed experimental results on ${\mathrm{D}}_2$, ${\mathrm{N}}_2$, and ${\mathrm{O}}_2$.