Production and properties of CO2 cluster anions

Evaporative cooling and reaction of carbon dioxide clusters by low-energy electron attachment

Anionic carbonate CO3- has been found in interstellar space and the Martian atmosphere, but its production mechanism is in debate so far. To mimic the irradiation-induced reactions on icy micrograins in the Martian atmosphere and the icy shell of interstellar dust, here we report a laboratory investigation on the dissociative electron attachments to the molecular clusters of CO2. We find that anionic species (CO2)n-1O- and (CO2)n- (n = 2, 3, 4) are produced in the concerted reaction and further stabilized by the evaporative cooling after the electron attachment. We further propose a dynamics model to elucidate their competitive productions: the (CO2)n- yields survive substantially in the molecular evaporative cooling at the lower electron attachment energy, while the reactions leading to (CO2)n-1O- are favored at the higher attachment energy. This work provides new insights into physicochemical processes in CO2-rich atmospheres and interstellar space.

The Surface Science of Catalysis and More, Using Ultrathin Oxide Films as Templates: A Perspective

Surface science has had a major influence on the understanding of processes at surfaces relevant to catalysis. Real catalysts are complex materials, and in order to approach an understanding at the atomic level, it is necessary in a first step to drastically reduce complexity and then systematically increase it again in order to capture the various structural and electronic factors important for the function of the real catalytic material. The use of thin oxide films as templates to mimic three-dimensional supports as such or for metal particles as well as to model charge barriers turns out to be appropriate to approach an understanding of metal-support interactions. Thin oxide films also exhibit properties in their own right that turn out to be relevant in catalysis. Thin oxide film formation may also be used to create unique two-dimensional materials. The present perspective introduces the subject using case studies and indicates possible routes to further apply this approach successfully.

Theoretical studies on clusters of carbonate with carbon dioxide, CO31–/2–(CO2)n, forn= 1–5 — Comparison of carbonate clusters with sulfate clusters

Density functional theory (DFT) calculations were performed on the geometries and energies of CO31–/2–(CO2)nclusters with n = 1–5. For small clusters (n = 1 or 2), coupled cluster energies were obtained. Up to three CO2molecules are bound covalently to the dianion. Only weak electrostatic bonds were found in the monoanions. Calculated binding energies for the monoanions are in reasonable agreement with experimental values. The calculated adiabatic electron detachment energy for the dianion is –0.07 eV at n = 5, indicating that at least six CO2molecules will have to be added to CO32–before the dianionic cluster becomes, in the gas phase, more stable than the monoanionic one. In comparison, for sulfate – carbon dioxide clusters, stabilization occurs at n = 2. Carbonate clusters are compared with sulfate clusters for three solvent molecules: CO2, SO2, and H2O. Carbonate clusters have larger binding energies than sulfate clusters. For a given dianion, binding energies are largest for SO2and smallest for H2O. However, in all cases, stabilization of the carbonate dianion by clustering is more difficult to achieve than stabilization of the sulfate dianion.

Electron photoemission from charged films: Absolute cross section for trapping 0–5eV electrons in condensed CO2

The electron trapping or attachment cross section of carbon dioxide (CO2) condensed as thin films on a spacer of Ar is obtained using a simple model for electron trapping in a molecular film and then charge releasing from the same film by photon absorption. The measurements are presented for different electron exposures and impact energies, film thicknesses, and probing photon energies. The cross section for trapping an electron of incident energy between 0 and 5 eV reveals three different attachment processes characterized by a maximum at about 0.75 eV, a structured feature around 2.25 eV, and a shoulder around 3.75 eV. From the measurement of their dependence with the probing photon energy, the two lowest processes produce traps having a vertical electron binding energy of approximately 3.5 eV, whereas the highest one yields a slightly higher value of approximately 3.7 eV. The 0.75 eV maximum corresponds to the formation of vibrational Feshbach resonances in (CO2)n- anion clusters. The 2.25 eV feature is attributed to the formation of a vibrationally excited 2Piu anion in (CO2)n- clusters, followed by fast decay into its vibrational ground state without undergoing autodetachment. Finally, 3.75 eV shoulder is assigned to the well-known dissociative electron attachment process from 2Piu anion state producing the O- anion in the gas phase and the (CO2)nO- anions in clusters.