Inelastic electron–dipole-molecule scattering at sub-milli-electron-volt energies: HF andNH3

Studies of destruction of very-high-n (100<n<400) Rydberg atoms in collisions with the polar targets HF and ${\mathrm{NH}}_3$ are reported. Analysis of the data using the essentially-free-electron model suggests that, for ultralow electron energies (∼80 μeV–1.4 meV), the cross section σ(ɛ) for rotationally inelastic scattering of electrons by a polar target varies approximately as 1/ɛ, where ɛ is the electron energy.