Dynamics of ferrocene in molecular sieves probed by Mossbauer spectroscopy and nuclear resonant scattering

A detailed study on the slow dynamics of ferrocene in the unidimensional channels of the molecular sieves SSZ-24 and AlPO4-5 has been carried out, using Mössbauer spectroscopy (MS), nuclear forward scattering (NFS) and synchrotron radiation-based perturbed angular correlations (SRPAC). In both host systems, anisotropic rotational dynamics is observed above 100 K. For SSZ-24, this anisotropy persists even above the bulk melting temperature of ferrocene. Various theoretical models are exploited for the study of anisotropic discrete jump rotations for the first time. The experimental data can be described fairly well by a jump model that involves reorientations of the molecular axis on a cone mantle with an opening angle dependant on temperature

Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering

Nuclear inelastic scattering of synchrotron radiation has been used now since 10 years as a tool for vibrational spectroscopy. This method has turned out especially useful in case of large molecules that contain a M\"ossbauer active metal center. Recent applications to iron-sulfur proteins, to iron(II) spin crossover complexes and to tin-DNA complexes are discussed. Special emphasis is given to the combination of nuclear inelastic scattering and density functional calculations

Confined phonons in glasses

We have applied nuclear inelastic absorption (NIA) to the molecular glass former dibutyl phthalate/ferrocene, both in bulk and in nanoporous matrices having pore sizes of 50 and 25 Å. The quantity g(E)/E 2, where g(E) is the vibrational density of states (VDOS) of the iron atoms, exhibits a pronounced maximum around 2 meV. Confinement in pores leads to a suppression of the VDOS below 1.5 meV, independent of the pore size. The influence of local interactions at the pore wall was assessed using Raman scattering. Our observations are discussed in the light of experimental and theoretical results on nanoparticles and for the Boson peak

Structure and dynamics of octamethyl-ethinyl-ferrocene: an organometallic rotator phase

The onset of dynamics and the structural changes of octamethyl- ethinyl-ferrocene around a solid-solid phase transition at 248 K have been investigated using the novel technique of quasielastic nuclear forward scattering (QNFS) in a temperature range between 61 and 257 K at a photon energy of 14.413 keV, as well as X-ray powder diffraction at various energies. A pronounced hysteresis for both the dynamical and the structural properties is observed and confirmed by differential-scanning calorimetry. We assign the observed phenomena to a first-order transition from a low-symmetry low-temperature phase to a high- symmetry high-temperature plastically crystalline phase with nearly cubic symmetry. Possible mechanisms for this transition are discussed in the light of our results. (C) 2003 Elsevier Science Ltd. All rights reserved

Comparison of quasi-Hartree-Fock wave-functions for lithium hydride

We compare the Hartree-Fock wave-functions for crystalline LiH obtained either with a standard Crystalline-Orbital-LCAO procedure or following the Adams-Gilbert-Kunz (AGK) prescription. Total energy, band-structure, reciprocal form factors [B(r)] are taken as a reference, for checking the quality of the wave-function. The influence of the inclusion of high angular-quantum-number functions in the AGK basis set is explored. © 1992

Quasielastic nuclear forward scattering as a background-free probe of slow glass dynamics in confined geometries

The microscopic dynamics of dibutylphthalate/ferrocene in nanoporous silica matrices with pore sizes of 25, 50, 75, and 200 Å, respectively, has been investigated in a temperature range between 70 and 200 K by nuclear resonant scattering of synchrotron radiation. The decay of the coherently forward scattered signal is enhanced owing to the diffusive motion of resonant nuclei on the timescale of the nuclear resonance lifetime. This enhancement contains information about the self-correlation function for a fixed wave vector k = 7.3 Å-1. In the viscous regime and for 25 Å pores the diffusional dynamics is clearly slowed down when compared to the bulk material