Abstract
The intramolecular conversion of CO2 to molecular oxygen is an exotic reaction, rarely observed even with extreme optical or electronic excitation means. Here we show that this reaction occurs readily when CO2 ions scatter from solid surfaces in a two-step sequential collision process at hyperthermal incidence energies. The produced O2 is preferentially ionized by charge transfer from the surface over the predominant atomic oxygen product, leading to direct detection of both O2+ and O2−. First-principles simulations of the collisional dynamics reveal that O2 production proceeds via strongly-bent CO2 configurations, without visiting other intermediates. Bent CO2 provides dynamic access to the symmetric dissociation of CO2 to C+O2 with a calculated yield of 1 to 2% depending on molecular orientation. This unexpected collision-induced transformation of individual CO2 molecules provides an accessible pathway for generating O2 in astrophysical environments and may inspire plasma-driven electro- and photo-catalytic strategies for terrestrial CO2 reduction.
Highlights
The dissociation of CO2 proceeds via multiple pathways depending on available energy
The convergent analysis and agreement among experiment, kinematics, and first-principles MD simulations presented in this work support a collision-induced mechanism for direct intramolecular conversion of CO2 to O2
With the dynamics evolving on the ground electronic state of neutral CO2, we find that O2 is formed via delayed fragmentation, where the delay results from atomic rearrangement of the colliding CO2 molecules into a strongly bent geometry
Summary
The dissociation of CO2 proceeds via multiple pathways depending on available energy. The partial dissociation reaction, CO2 → CO + O (3P or 1D), has the lowest energy requirement (5.43 or 7.56 eV)[10]; it has been extensively studied in photochemistry and in heterogeneous catalysis under thermal activation conditions[11,12]. Other pathways may be possible at intermediate energies, such as the exotic reaction: CO2 → C(3P) + O2(1Σg), which entails extensive intramolecular rearrangement of the CO2 molecule. The first step in this channel involves bending of the CO2 molecule to bring the two O atoms in close proximity, which requires close to 6 eV of internal energy[13]. Inaccessible by thermal activation, transitions to electronically excited and anionic states of CO2 can bend the molecule as a first step to O2 production. The reaction may be relevant for astrophysical environments, such as comets, moons, and planets with CO2 atmospheres
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