Dissociative electron attachment to formamide: Direct and indirect pathways from resonant intermediates

Dissociative electron attachment (DEA) to formamide (HCONH2), the smallest molecule with a peptide bond, is investigated with electron-molecule scattering calculations. At the equilibrium geometry we identify two resonances of A" and A' symmetry at 3.77 and 14.90 eV, respectively. To further assess potential bond-breaking pathways for the transient negative ions (TNIs), the behavior of the resonances upon bond stretching of the C-H and C-N bond is investigated. While along the C-H dissociation coordinate neither resonance changes significantly, we find instead that both resonances are stabilized upon stretching the peptide C-N bond, with their resonance energy and width coming down rapidly, most strongly so for the A' resonance. The A' resonance is thus seen to disappear when the C-N bond is stretched for more than 1 A, where it presumably smoothly connects to a bound anion state, a direct DEA pathway for the Å TNI to yield NH 2- and HCO. The A" resonance is found instead not to be purely dissociative along the C-N coordinate but to evolve into forming a low-lying resonance on the NH2 fragment. Furthermore, symmetry considerations dictate here that the incoming electron attaches itself to an orbital of A' symmetry of the NH2- and HCO asymptotic fragments. Therefore, DEA from the A" TNI has to occur via a symmetry-breaking, nonadiabatic curve crossing which connects to the purely dissociative A' metastable anionic state that is coming down in energy as the bond stretching occurs. © 2009 American Chemical Society.