Inelastic electron-dipole-molecule scattering at sub-milli-electron-volt energies: CH3I and CH2Br2.

Abstract

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 (\ensuremath{\sim}80 \ensuremath{\mu}eV to 1 meV), the cross section \ensuremath{\sigma}(\ensuremath{\varepsilon}) for rotationally inelastic scattering of electrons by a polar target varies approximately as 1/\ensuremath{\varepsilon}, where \ensuremath{\varepsilon} 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.