Sulfur in different chemical surroundings – S K XANES spectra of sulfur-containing heterocycles and their quantum-chemically supported interpretation Original Research Article

The excited states in the XANES region of 2-mercaptobenzooxazole and 2-mercaptobenzothiazole and of their sulfur-bridged dimeric analogues were investigated at the sulfur 1s-ionization threshold by means of synchrotron radiation. The electronic excitations were treated employing density functional theory calculations. The theoretical results obtained for the planar monomers and the bent dimers are in good accordance with the experimental spectra. They allow the assignment of the spectral structures in the region of the S 1s-electron binding energy to π* and σ* resonances involving orbitals of the >CS and –C–Sx–C– (x=1,2) moieties of the molecules. The results are discussed in terms of antibonding π* and σ* interactions between the sulfur and the neighboring carbon atoms and of the symmetric and antisymmetric combinations of the respective σ* orbitals of the monomeric units.