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 π* 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°. 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.