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 dep endence of the dissociative attachment process CCl4 fe --> Cl- + CCl3 (at electron energies between threshold and 2 eV) in a target gas temp erature range of 300-500 K. With the available high energy resolution of about 11 meV FWHM from an improved trochoidal electron monochromato r it was possible to investigate in a single collision crossed beam ex periment the true electron energy dependence of the cross-section of t his s-wave electron capture process down to the limiting E(-1/2) behav ior. At energies above approximately 20 meV the cross-section decrease s more strongly towards higher energies, exhibiting around 100 meV the typical E(-1) behavior predicted for the s-wave de Broglie cross-sect ion. Additional structure above 200 meV is interpreted in terms of aut odetachment and a peak at around 0.8 eV (with a peak height of approxi mately 0.3% of that of the zero energy peak) is attributed to the trip ly degenerate T-2(2) excited state resonance. No temperature dependenc e of the measured cross-section function could be observed in the inve stigated temperature range of 300-500 K.