Tautomeric structure of N-salicylideneaniline derivatives studied by soft X-ray absorption spectroscopy and X-ray photoelectron spectroscopy

The tautomeric structures in solid phase were studied by near-edge X-ray ab sorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) for five N-salicylideneaniline derivatives. The observed features in the N EXAFS spectra were assigned by (1) the comparison with the core excitation spectra of reference compounds and (2) ab initio MO calculations of the cor e-excited states by the improved virtual orbital method. The relative inten sity of the observed peaks characteristic of each tautomer enabled us to de duce the tautomeric structures of these compounds. The XPS spectra allowed quantitative estimation of the relative tautomer populations. These structu res are consistent with the previous estimation by Xray diffraction. These results demonstrate the usefulness of NEXAFS as well as XPS for studying th e tautomerism in hydrogen bonded systems.