Nitrogen K-shell excitations in complex molecules and polypyrrole

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-benzylidene-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 N1s 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 N1s(-1)2p resonance in NK XANES formation in all compounds under study. The influence of the electronic charge transfer, bond conjugation and localization on the energies and intensities of pi* and sigma* 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.