Electron transfer, harpooning, reagent orientation, and chemical intuition

Our chemical 'intuition' tells us that a molecule will react only if certain sites are attacked. To test this notion we have oriented molecules and reacted them in crossed molecular beams. We find that reactivity depends on reagent orientation and the 'harpoon' mechanism provides an explanation for much of the observed behavior. A Donor atom transfers an electron to an electrophilic Acceptor creating an unstable transient negative ion which dissociates in the direction the molecule is oriented. Ions may or may not recombine to form neutrals depending on the collision energy and the orientation. The electron is transferred to an orbital of the Acceptor (LUMO at low energy) and this transfer depends on the spatial extent of the LUMO. The nascent donor ion can perturb the transient negative ion giving different ions from those observed in attachment of free electrons.