In search of covalently bound tetra- and penta-oxygen species: a photoelectron spectroscopic and Ab initio investigation of MO4- and MO5- (M = Li, Na, K, Cs)

Cesium's Off-the-Map Valence Orbital

The Td -symmetric [CsO4 ]+ ion, featuring Cs in an oxidation state of 9, is computed to be a minimum. Cs uses outer core 5s and 5p orbitals to bind the oxygen atoms. The valence Cs 6s orbital lies too high to be involved in bonding, and contributes to Rydberg levels only. From a molecular orbital perspective, the bonding scheme is reminiscent of XeO4 : an octet of electrons to bind electronegative ligands, and no low-lying acceptor orbitals on the central atom. In this sense, Cs+ resembles hypervalent Xe.

Tetraoxygen on reduced TiO2(110): oxygen adsorption and reactions with bridging oxygen vacancies

Oxygen adsorption on reduced TiO2(110) is investigated using temperature programmed desorption and electron-stimulated desorption. At low temperatures, 2 O(2) molecules can be chemisorbed in each oxygen vacancy. These molecules do not desorb upon annealing to 700 K. Instead, for 200 K<T<400 K, the 2 O(2) convert to another species, which has four oxygen atoms, i.e., tetraoxygen, that decomposes at higher temperatures. In contrast, when only 1 O(2) is adsorbed in an oxygen vacancy, the molecule dissociates upon annealing above ~150 K to heal the vacancy in agreement with previous results.

The Oxygen-Rich Carboxide Series: COn (n = 3, 4, 5, 6, 7, or 8)

The lowest-energy isomers of the high-order carboxide series, COn (n = 3-8), have been elucidated via ab initio quantum chemical calculations. The structures of the lowest order of these (3 and 4) are in close agreement with previous calculations and with experimental data. The structures of the higher-order species are elucidated and correlated to the previous structures, showing similarities in structure and reactivity pathways. The reaction energies of the formation of all products are shown to be related. Exothermic pathways of formation often involve a C2v form of CO2, which was shown to be metastable. The newly identified species could be intermediates in atmospheric reactions. The calculated vibrational frequencies and IR intensities may be used to identify these metastable species.

Ab Initio Probing of the Aromatic Oxygen Cluster O42+

The structure of the O(4)(2+) dication has been studied theoretically using a few conventional theoretical methods. We found the O(4)(2+) dication to be a metastable species with a perfect square structure. The molecular orbital analysis reveals that this dication is the first all-oxygen aromatic system with 6pi electrons. Although the O(4)(2+) dication is highly thermodynamically unstable, we believe that appropriate counteranions with very high electron detachment energy (superhalogens) can be found to form a solid-state compound containing O(4)(2+). Another way to probe the planar aromatic tetra oxygen dication could be a double-photoionization process of the (O(2))(2) dimer.

Ozonic Acid and Its Ionic Salts: Ab Initio Probing of the O42- Dianion

The pyramidal O(4)(2)(-) dianion is valence isoelectronic to the well-known ClO(3)(-) and SO(3)(2)(-) anions, and yet it has not been observed. The synthesis of any molecule containing such a dianion would represent a major breakthrough in making molecules containing more than three covalently bound oxygen atoms. We found that the parent H(2)O(4) ozonic acid is unstable in the form of the valence isoelectronic sulfurous acid H(2)SO(3). Our quantum chemical probing of the Li(2)O(4) ionic salt molecule is inconclusive. However, we found that the specially designed FLi(3)O(4) gas phase molecule is a true metastable species and could be considered as the first molecule containing the O(4)(2)(-) dianion. Our theoretical prediction of the first compound containing the tetraatomic covalently bound O(4)(2)(-) dianion opens the possibility to even more oxygen rich compounds, which will have a great potential as high density oxygen storage.