Density Functional Theory is applied to understand the large difference in surface reactivity of LiCoO 2 due to Al/Co substitution which is experimentally observed. In this way, we explore the SO 2 and CO 2 adsorption modes on the (110) surface of LiCoO 2 and α-LiAlO 2 . For SO 2 adsorption, chemisorption produces sulfite species (for LiCoO 2 and α-LiAlO 2 ) and sulfate species (in the case of LiCoO 2 ). We demonstrate that the modification of the surface reactivity when Co 3+ ions are substituted by Al 3+ ions is due to a change from an adsorption mode controlled by redox properties for LiCoO 2 to a less energetically favorable adsorption mode controlled by acid−base properties for α-LiAlO 2 . For CO 2 adsorption, the formation of carbonate species is observed for both compounds, illustrating the fundamental difference in the factors controlling SO 2 adsorption compared to CO 2 adsorption.

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The optimized geometries of oxysulfur compounds derived from dimethyl disulfide were calculated at the MP2/6-31G* level, and the relative energies of isomers in the CH 3 S 2 OCH 3 , CH 3 S 2 O 2 CH 3 , CH 3 S 2 O 3 CH 3 , and CH 3 S 2 O 4 CH 3 series were compared. All these derivatives are characterized by long S-S bonds or long sulfenyl or sulfinyl S-O bonds for sulfur-oxygen-bridged isomers. According to the geometrical parameters calculated for vic-disulfoxide 4RR in the CH 3 S 2 O 2 CH 3 series, this compound is better described as two interacting sulfinyl radicals, and the obtained results substantiate the experimental scheme proposed by Clennan 28 for the intramolecular singlet oxygen addition on disulfides. The UV spectra of all these isomers were evaluated at a standard ab initio level: despite underestimated wavelengths, their evolution (wavelengths and molar extinction coefficients) is consistent with experiment and indicates a strong influence of the σ S-S ,n S f σ* S-S transition for sulfur-sulfur-bridged isomers and of n S ,n O f σ* S-O transitions for sulfur-oxygenbridged isomers. As a result, these compounds will be cleaved photochemically by S-S or alternatively by sulfenyl or sulfinyl S-O bond cleavage, leading to oxysulfur radicals. The numerous experimental data on oxysulfur molecules and radicals are discussed in light of the predicted stability and photochemical reactivity of both classes of molecules. The validity of this standard method of evaluation of UV spectra was further assessed by a more accurate calculation on a known stable model compound, methyl methanethiosulfinate (2), by use of an extensive configuration interaction treatment (MRSDCI formalism).