title: Ultrafast 2DIR spectroscopy of ferric azide precursors for high-valent iron. Vibrational relaxation, spectral diffusion, and dynamic symmetry breaking.
abstract: Femtosecond mid-infrared pump-probe and two-dimensional mid-infrared spectroscopy have been used to investigate the dynamics of vibrational relaxation and vibrational spectral diffusion of the asymmetric N3-stretching vibration of pseudo-octahedral azidoiron(III) complexes, [L6-nFe(N3)n](+) with n = 1 or 2 and L being an auxiliary ligand of denticity 6-n, in acetonitrile at room temperature. Compared to the free azide anion in acetonitrile solution, the vibrational relaxation dynamics are considerably accelerated. Vibrational energy transfer to the solvent is accelerated by virtue of a resonance with an overtone transition of the solvent. Intramolecular vibrational redistribution is found to be accelerated by virtue of a coupling between the initial azide stretching vibration and the torsional modes involving the axial ligands. Vibrational spectral diffusion within the asymmetric N3-stretching resonance was found to be insensitive to solvent fluctuations because the axial azide ligands are only partially accessible to the solvent. The particular role of intramolecular structural relaxations of the complex for shaping the linear and nonlinear two-dimensional infrared spectra is discussed in terms of ultrafast symmetry-breaking torsional fluctuations and on the basis of density functional theory calculations.
authors.affiliation: Abteilung für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany.
authors.forename: Denis
authors.initials: D
authors.lastname: Czurlok
authors.affiliation: Abteilung für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany.
authors.forename: Joel
authors.initials: J
authors.lastname: Torres-Alacan
authors.affiliation: Abteilung für Molekulare Physikalische Chemie, Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Vöhringer
mesh_terms: D001386:Azides / Q000737:chemistry*; D004058:Diffusion; D005290:Ferric Compounds / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D013055:Spectrophotometry, Infrared; D013997:Time Factors; D014732:Vibration
chemical_list: D001386:Azides; D005290:Ferric Compounds