Low-energy behavior of exothermic dissociative electron attachment - art. no. 022706

We discuss two models for electron attachment to molecules: the Vogt-Wannie r model for capture into a polarization well and the resonance model for di ssociative attachment. The Vogt-Wannier model is generalized for the case o f a target with a permanent dipole moment, and results are presented for di ssociative attachment to CH3I. It is shown that the resonance theory should incorporate in this case a weakly bound dipole-supported state of CH3I-, w hereas the generalized Vogt-Wannier theory gives a reasonable estimate for the cross section in the meV and sub-meV region. The Vogt-Wannier model is also applied to the process of attachment to SF6, CCl4, and C-60. In the fi rst case the s-wave capture model provides a satisfactory description of th e experimental data for energies below the first vibrational excitation thr eshold, whereas for CCl4 it underestimates the attachment cross section by a factor of 2 in the sub-meV region. For C-60 we suggest that electron atta chment is dominated by s-wave capture in the region below 2 meV and by p-wa ve capture in the energy range above 4 meV. Our model reproduces data for R ydberg electron and free-electron attachment observed in beam experiments. It is, however, at variance with the strong rise of the attachment rate coe fficients with electron temperature observed in flowing afterglow-Langmuir probe measurements.