Until recently, it was widely regarded that only one reaction pathway led to the production of molecular oxygen in Earth's prebiotic primitive atmosphere: a three-body recombination reaction of two oxygen atoms and a third body that removes excess energy. However, an additional pathway has recently been observed that involves the photodissociation of CO2 on exposure to ultraviolet light. Here we demonstrate a further pathway to O2 production, again from CO2, but via dissociative electron attachment (DEA). Using anion-velocity image mapping, we provide experimental evidence for a channel of DEA to CO2 that produces O2(X(3)Σ(-)g) + C(-). This observed channel coexists in the same energy range as the competitive three-body dissociation of CO2 to give O + O + C(-). The abundance of low-energy electrons in interstellar space and the upper atmosphere of Earth suggests that the contributions of these pathways are significant and should be incorporated into atmospheric chemistry models.

Dissociation dynamics of the temporary negative ions of ethanol and acetaldehyde formed by the low-energy electron attachments is investigated by using the anion velocity map imaging technique and ab initio molecular dynamics simulations. The momentum images of the dominant fragments O(-)/OH(-) and CH3 (-) are recorded, indicating the low kinetic energies of O(-)/OH(-) for ethanol while the low and high kinetic energy distributions of O(-) ions for acetaldehyde. The CH3 (-) image for acetaldehyde also shows the low kinetic energy. With help of the dynamics simulations, the fragmentation processes are qualitatively clarified. A new cascade dissociation pathway to produce the slow O(-) ion via the dehydrogenated intermediate, CH3CHO(-) (acetaldehyde anion), is proposed for the dissociative electron attachment to ethanol. After the electron attachment to acetaldehyde molecule, the slow CH3 (-) is produced quickly in the two-body dissociation with the internal energy redistributions in different aspects before bond cleavages.

Three spin-orbit states, 12Π1/2, 22Π3/2, and 22Π1/2, of chloroiodine anion (ICl−) formed by low-energy electron attachment in the Franck-Condon region are associated with the dissociative limits of I− (1S0) and Cl (2P3/2) or Cl* (2P1/2) fragments. Within the adiabatic scheme, the presumptive Π-symmetry of the fragment angular distributions is dramatically changed to be the Π-Σ mixing symmetry, due to the significant spin-orbit interaction effect on the electronic state couplings of ICl−. The present experimental approach also enables us to separate the contributions of different electronic states from the mixed states, providing a crucial method for quantitatively evaluating the configuration-interaction wavefunctions.