Nitrogen K-shell excitations in complex molecules and polypyrrole Original Research Article

Experimental and theoretical studies of nitrogen K-shell near-edge absorption in complex compounds such as thiourea, benzalaniline, pyrrole, polypyrrole, tetraethylammonium, tetrabutylammonium and substituted 2-hydroxy-3-methoxy-benzyl-idene-aniline compounds were carried out. The quasi-atomic model was used in order to calculate the spectral distribution of oscillator strengths for transitions from the N 1s level to excited discrete and continuum states, to explain general trends in the changes of K-shell excitation spectra and to reveal their relationships with chemical bonding of the N atom in the compounds. The performed analysis of theoretical and experimental spectra evidences the central role of splitting of an intense N 1s−12p resonance in N K XANES formation in all compounds under study. The influence of the electronic charge transfer, bond conjugation and localization on the energies and intensities of π∗ and σ∗ resonances are discussed in detail. The strong connection between interference and chemical bonding effects on the main resonance features of X-ray absorption in the compounds under study is revealed.