Dissociative electron attachment to CO2 produces molecular oxygen

Abstract

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.

Direct dioxygen evolution in collisions of carbon dioxide with surfaces

“…Specifically, the mechanism differs from that of photochemical interconversion 14 not only in terms of activation (collisional vs. photochemical) but also because the collisional mechanism occurs via a delayed fragmentation of a single CO 2 intermediate, i.e., without visiting the linear COO state. The collisional mechanism also differs fundamentally from that taking place in electron-attachment experiments 17 , where the CO 2 bends spontaneously on the anionic potential energy surface. Instead, the bent CO 2 state is accessed on the neutral surface via collisional energy transfer.…”

“…Although inaccessible by thermal activation, transitions to electronically excited and anionic states of CO 2 can bend the molecule as a first step to O 2 production. Indeed, pioneering experiments employing VUV photo-excitation 14–16 and electron attachment 17,18 have shown that dissociation of CO 2 into C( 3 P) + O 2 (X 3 Σ g − ) is possible, as evidenced by the detection of the complementary atomic C + or C − fragment. Further confirmation of the exotic pathway, however, remained elusive as neutral or ionized O 2 products were not detected.…”

Nonadiabatic dynamics in multidimensional complex potential energy surfaces

“…From all the above-mentioned processes that can be formulated in terms of a complex-valued Hamiltonian, we have chosen to survey a DEA reaction as the rst application of our proposed methodology. DEA is known to play important roles, to a greater or lesser degree, in DNA damage induced by ionizing radiation, 32,33 in the action of radiosensitizing drugs, 33,34 in the chemical evolution of interstellar media 35 and planetary atmospheres, 36,37 in plasma technologies, 38 among many other examples. 19,39 Of particular relevance herein, low energy electrons can very efficiently promote DEA reactions in halogen-containing unsaturated compounds.…”

Intramolecular water-splitting reaction in single collisions of water ions with surfaces

“…9 For example, molecular O 2 has been produced directly from CO 2 in the gas-phase by VUV photolysis and also by dissociative electron attachment with an electron energy between 15.9 and 19 eV. 10,11 Such reaction pathways are not accessible using thermal energy; rather, they require photonic, electronic, or even nuclear excitation means. We show here another unexplored way to drive such reactions by means of gas-surface collisions at hyperthermal incidence energies (60–300 eV).…”