Reaction and Scattering in Cold Electron Collisions

Experimental data are presented for the scattering of electrons by ${\mathrm{C}\mathrm{C}\mathrm{l}}_4$ between 8 and 200 meV impact energy. These results are used in conjunction with data for the reactive process, yielding ${\mathrm{C}\mathrm{l}}^{-}$, to study the low energy behavior of a system which simultaneously displays both reactive and elastic scattering channels. Phase shifts are derived and illustrate how channel competition develops as the energy falls. This behavior and the involvement of vibronic effects at impact energies above $\sim 30\mathrm{m}\mathrm{e}\mathrm{V}$ pose a challenge to theory.

Figure 1

Total integral ${\sigma }_{T,I}$ (upper set) and backward ${\sigma }_{T,B}$ cross sections (lower set) for scattering of electrons by ${\mathrm{C}\mathrm{C}\mathrm{l}}_4$ as a function of electron impact energy. Errors in the cross sections are $\pm 8\%$ at the lowest energies, falling to $\pm 5\%$ at energies above $\sim 20\mathrm{m}\mathrm{e}\mathrm{V}$.

Figure 2

Elastic integral ${\sigma }_I^{\mathrm{e}\mathrm{l}}$ (upper set) and backward ${\sigma }_B^{\mathrm{e}\mathrm{l}}$ scattering cross sections (lower set) for scattering of electrons by ${\mathrm{C}\mathrm{C}\mathrm{l}}_4$ as a function of electron impact energy. Errors in the cross sections are $\pm 8\%$ at the lowest energies, falling to $\pm 5\%$ at energies above $\sim 20\mathrm{m}\mathrm{e}\mathrm{V}$. The curves show the result of fitting using Eqs. (3, 4), as described in the text.

Figure 3

$s$-wave (solid circles) and $p$-wave (open circles) phase shifts for $e^{-}+{\mathrm{C}\mathrm{C}\mathrm{l}}_4$ reactive and elastic scattering derived from fitting procedures described in the text. Errors associated with the phase shifts are $\pm 5\%$.