Inelastic electron–dipole-molecule scattering at sub-milli-electron-volt energies: ${\mathrm{CH}}_3$I and ${\mathrm{CH}}_2$${\mathrm{Br}}_2$

Studies of Rydberg-atom destruction in collisions with the polar targets ${\mathrm{CH}}_3$I and ${\mathrm{CH}}_2$ ${\mathrm{Br}}_2$ for values of principal quantum number n in the range 100–400 are reported. Analysis of the data using the essentially-free-electron model suggests that, for ultralow electron energies (∼80 μeV to 1 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. The Born approximation does not predict such behavior at very low collision energies, and possible reasons for this discrepancy are discussed.