With the DFT transition state approximation (DFT-TS) researchers from Trieste have calculated the fine structure near the K absorption edge of C and N atoms in free (H2), Cu, and Ni phthalocyanines (Pc). When core hole relaxation effects are included, DFT-TS can yield accurate K-shell excitation spectra.
The simulated NEXAFS spectra compare well with experimental data. The core excitations, governed by s→p dipole transitions, are calculated for each symmetry-unequivalent atom, thereby enabling the assignment of specific spectral features.
Especially the N K-edge spectrum is sensitive to the presence and nature of a central metal atom, to which the pyrrolic N atoms are directly bound, making NEXAFS a sensitive tool to study metallophthalocyanines.
Calculated (solid line) and experimental (dashed line) NEXAFS spectrum for N atoms in Ni-phthalocyanine. The individual contributions from the aza (red) and pyrrole (blue) nitrogen atoms are indicated with vertical lines.
Near-Edge X-ray Absorption Spectroscopy, core excitations, diffuse basis sets, PDOS
R. De Francesco, M. Stener, and G. Fronzoni, Theoretical Study of Near-Edge X-ray Absorption Fine Structure Spectra of Metal Phthalocyanines at C and N K-Edges J. Phys. Chem. A, 116 2885-2894 (2012).Key conceptsbonding analysis inorganic chemistry XAS