A CROSSED-BEAM HIGH-RESOLUTION STUDY OF DISSOCIATIVE ELECTRON-ATTACHMENT TO CCL4

Using a crossed electron/molecule beam ion source in combination with a quadrupole mass spectrometer we have studied the electron energy dependence of the dissociative attachment process CCl4 fe --> Cl- + CCl3 (at electron energies between threshold and 2 eV) in a target gas temperature range of 300-500 K. With the available high energy resolution of about 11 meV FWHM from an improved trochoidal electron monochromator it was possible to investigate in a single collision crossed beam experiment the true electron energy dependence of the cross-section of this s-wave electron capture process down to the limiting E-1/2 behavior. At energies above approximately 20 meV the cross-section decreases more strongly towards higher energies, exhibiting around 100 meV the typical E-1 behavior predicted for the s-wave de Broglie cross-section. Additional structure above 200 meV is interpreted in terms of autodetachment and a peak at around 0.8 eV (with a peak height of approximately 0.3% of that of the zero energy peak) is attributed to the triply degenerate T-2(2) excited state resonance. No temperature dependence of the measured cross-section function could be observed in the investigated temperature range of 300-500 K.