DISSOCIATIVE ATTACHMENT AS A PROBE OF THE DISTANCE DEPENDENCE OF INTRAMOLECULAR ELECTRON-TRANSFER

The dissociative attachment (DA) cross section for Cl- production in 3 , a molecule with ethylenic and C-CL groups separated by about 5.8 Ang strom, is measured and found to be 6.5 times smaller than that for 2, in which the two functional groups are separated by only 3.4 Angstrom. As in 2, the energy of the peak in the DA cross section coincides wit h that for electron attachment into the pi orbital. These results sho w that the DA process can be used to probe the distance dependence of the electronic coupling between remote functional groups of gas-phase molecules. For 3, unlike 2, the DA spectrum displays a high-energy sho ulder in addition to the main peak. We interpret this in terms of two competing DA channels: one arising from direct electron capture into t he C-Cl sigma orbital and the other involving a pi*,sigma* coupling m echanism. In the latter process, the intramolecular electron transfer takes place in a time comparable to that required for the C-Cl bond le ngth to stretch from its equilibrium value to that at the crossing poi nt of the anionic surfaces.