Orientational probing of multilayer 2-mercaptobenzoxazole through NEXAFS:: An experimental and theoretical study

Near edge X-ray absorption fine structure (NEXAFS) spectra of 2-mercaptobenzoxazole have been investigated from experimental and theoretical points of view, The 2-mercaptobenzoxazole molecule presents an interesting case for NEXAFS, with its aromatic, benzene-like, fragment and its heteroatom-rich part, containing C, N, O, and S atoms. NEXAFS spectra of a 2-mercaptobenzoxazole multilayer on Pt(111) at the carbon, nitrogen, and oxygen K-edges and at the sulphur L-edge have been recorded at normal and grazing incidence angles of the photon beam with respect to the surface. The C, N, and O K-edge spectra exhibit angular dependence in the pi* resonance region, indicating a mean orientation of the molecules on the surface. The angle between the molecular plane and the surface has been found to be about 48 degrees. The experimental data are discussed by comparison with static-exchange (STEX) ab initio calculations for the different edges. Good agreement is observed between experiment and theory, allowing for a detailed discussion and attribution of the various features observed. A vibrational progression at the C K-edge is also identified in the highly resolved experimental spectrum.