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Negative ion photoelectron spectroscopy confirms the prediction that D_3h carbon trioxide (CO₃) has a singlet ground state.

ABSTRACT: The CO₃ radical anion (CO₃?^-) has been formed by electrospraying carbonate dianion (CO₃^2-) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO₃?^- shows that, unlike the isoelectronic trimethylenemethane [C(CH₂)₃], D_3h carbon trioxide (CO₃) has a singlet ground state. From the NIPE spectrum, the electron affinity of D_3h singlet CO₃ was, for the first time, directly determined to be EA = 4.06 ± 0.03 eV, and the energy difference between the D_3h singlet and the lowest triplet was measured as ?E_ST = - 17.8 ± 0.9 kcal mol^-1. B3LYP, CCSD(T), and CASPT2 calculations all find that the two lowest triplet states of CO₃ are very close in energy, a prediction that is confirmed by the relative intensities of the bands in the NIPE spectrum of CO₃?^-. The 560 cm^-1 vibrational progression, seen in the low energy region of the triplet band, enables the identification of the lowest, Jahn-Teller-distorted, triplet state as ³A₁, in which both unpaired electrons reside in ? MOs, rather than ³A₂, in which one unpaired electron occupies the b₂ ? MO, and the other occupies the b₁ ? MO.

SUBMITTER: Hrovat DA

PROVIDER: S-EPMC5975725 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Negative ion photoelectron spectroscopy confirms the prediction that D3h carbon trioxide (CO3) has a singlet ground state.

Hrovat David A DA Hou Gao-Lei GL Chen Bo B Wang Xue-Bin XB Borden Weston Thatcher WT

Chemical science 20151113 2

The CO3 radical anion (CO3˙-) has been formed by electrospraying carbonate dianion (CO32-) into the gas phase. The negative ion photoelectron (NIPE) spectrum of CO3˙- shows that, unlike the isoelectronic trimethylenemethane [C(CH2)3], D3h carbon trioxide (CO3) has a singlet ground state. From the NIPE spectrum, the electron affinity of D3h singlet CO<s ...[more]

PMID: 29910870

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Project description:Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H2) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO3-? and (La,Sr)CrO3-? based perovskite-type electrodes was studied during electrochemical CO2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO2 reduction. In contrast to water splitting, the CO2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view.

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Negative ion photoelectron spectroscopy confirms the prediction that D_3h carbon trioxide (CO₃) has a singlet ground state.

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Negative ion photoelectron spectroscopy confirms the prediction that <i>D</i><sub>3h</sub> carbon trioxide (CO<sub>3</sub>) has a singlet ground state.

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