Sulfur in different chemical surroundings - SK XANES spectra of sulfur-containing heterocycles and their quantum-chemically supported interpretation

The excited states in the XANES region of 2-mercaptobenzooxazole and 2-merc aptobenzothiazole and of their sulfur-bridged dimeric analogues were invest igated at the sulfur ls-ionization threshold by means of synchrotron radiat ion. The electronic excitations were treated employing density functional t heory calculations. The theoretical results obtained for the planar monomer s 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 pi* and sigma* resonances involving orbital s of the >C=S and -C-S-x-C-(x = 1, 2) moieties of the molecules. The result s are discussed in terms of antibonding pi* and sigma* interactions between the sulfur and the neighboring carbon atoms and of the symmetric and antis ymmetric combinations of the respective sigma* orbitals of the monomeric un its. (C) 2001 Elsevier Science B.V. All rights reserved.