title: Assignment of near-edge x-ray absorption fine structure spectra of metalloporphyrins by means of time-dependent density-functional calculations.
abstract: The C 1s and N 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of three prototype tetraphenyl porphyrin (TPP) molecules are discussed in the framework of a combined experimental and theoretical study. We employ time-dependent density-functional theory (TDDFT) to compute the NEXAFS spectra of the open- and closed-shell metalloporphyrins CoTPP and ZnTPP as well as the free-base 2HTPP in realistic nonplanar conformations. Using Becke's well-known half-and-half hybrid functional, the computed core excitation spectra are mostly in good agreement with the experimental data in the low-energy region below the appropriate ionization threshold. To make these calculations feasible, we apply a new, simple scheme based on TDDFT using a modified single-particle input spectrum. This scheme is very easy to implement in standard codes and allows one to compute core excitation spectra at a similar cost as ordinary UV/vis spectra even for larger molecules. We employ these calculations for a detailed assignment of the NEXAFS spectra including subtle shifts in certain peaks of the N 1s spectra, which depend on the central coordination of the TPP ligand. We furthermore assign the observed NEXAFS resonances to the individual molecular subunits of the investigated TPP molecules.
authors: Department Chemie und Pharmazie, Lehrstuhl für Physikalische Chemie II and ICMM, Universität Erlangen-Nurnberg, Egerlandstrasse 3, 91058 Erlangen, Germany.
authors: Norman
authors: N
authors: Schmidt
authors: Rainer
authors: R
authors: Fink
authors: Wolfgang
authors: W
authors: Hieringer
mesh_terms: D003198:Computer Simulation; D008665:Metalloporphyrins / Q000737:chemistry*; D008968:Molecular Conformation; D013052:Spectrometry, X-Ray Emission / Q000379:methods*; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: D008665:Metalloporphyrins