Search results for "RELAXATION"
showing 10 items of 1162 documents
Electrochemical capacitance spectroscopy and capacitive relaxation of the changeover process in iron hexacyanoferrate molecular compound
2010
Abstract In this work it was proposed the use electrochemical capacitance spectroscopy (ECS) to evaluate the storage process during changeover in FeHCF compound. The approach is equivalent to electrochemical impedance spectroscopy (EIS) albeit from such analysis it was possible to focus attention on the capacitive and dielectric relaxation instead of the dispersive relaxation related to charge transfer. From such approach it was possible to obtain complementary information on the role played by [Fe 2+ (CN) 6 ] 4− vacancies during the changeover process. It was observed that Fe 3+ (NC) 5 OH − clusters located in these vacancies mediate an electronic and ionic coupled trapping/detrapping proc…
Low-temperature methyl group dynamics of hexamethylbenzene in crystalline and glassy matrices as studied by 2H NMR
1991
Abstract 2 H NMR spectra of hexamethylbenzene (HMB) in protonated crystalline and amorphous matrices at low temperatures are presented. All spectra reveal lineshape changes which can be attributed to methyl group tunnelling. Compared to neat HMB, a drastic increase of the tunnelling frequency is found for all systems. This indicates that the hindering potential originates predominantly from intermolecular forces. We studied the temperature dependence of these spectra and the spin-lattice relaxation in order to exclude a distribution of motional correlation times describing a thermally activated process. In addition, we find a distortion of the methyl tetrahedron.
Femtosecond Transient Absorption Study of the Dynamics of Acrylodan in Solution and Attached to Human Serum Albumin
2003
The excited-state relaxation dynamics of the protein-labeling dye acrylodan in solution and attached to human serum albumin has been studied by femtosecond transient absorption spectroscopy. Time-resolved spectra and kinetics of stimulated emission and excited-state absorption in the wavelength region from 400 to 800 nm were studied in ethanol and dimethylformamide. The excited-state solvation dynamics is characterized by multiexponential behavior in both solvents. In ethanol solution, the time dependence of the transient spectra is interpreted in terms of fast solvent relaxation followed by excited-state isomerization of the dye. Acrylodan attached to the protein shows a relaxation compone…
Experimental evidence for fractional time evolution in glass forming materials
2002
The infinitesimal generator of time evolution in the standard equation for exponential (Debye) relaxation is replaced with the infinitesimal generator of composite fractional translations. Composite fractional translations are defined as a combination of translation and the fractional time evolution introduced in [Physica A, 221 (1995) 89]. The fractional differential equation for composite fractional relaxation is solved. The resulting dynamical susceptibility is used to fit broad band dielectric spectroscopy data of glycerol. The composite fractional susceptibility function can exhibit an asymmetric relaxation peak and an excess wing at high frequencies in the imaginary part. Nevertheless…
Molecular scale structure and dynamics at an ionic liquid/electrode interface.
2017
After a century of research, the potential-dependent ion distribution at electrode/electrolyte interfaces is still under debate. In particular for solvent-free electrolytes such as room-temperature ionic liquids, classical theories for the electrical double layer are not applicable. Using a combination of in situ high-energy X-ray reflectivity and impedance spectroscopy measurements, we determined this distribution with sub-molecular resolution. We find oscillatory charge density profiles consisting of alternating anion- and cation-enriched layers at both cathodic and anodic potentials. This structure is shown to arise from the same ion-ion correlations dominating the liquid bulk structure.…
A Diferrous Single‐Molecule Magnet
2007
The diferrous complex [Fe2(acpypentO)(NCO)3] (1),(acpypentO– = the anion of 1,5-bis[2-pyridyl(1-ethylimino)]pentane-3-ol) was studied by spectroscopic (dual-mode X-band EPR and 57Fe-Mossbauer) and magnetic (AC magnetic susceptibility) techniques. Complex 1 (A. K. Boudalis et al., Inorg. Chem.2004, 43, 1574) was previously shown to exhibit an intramolecular ferromagnetic coupling with important single-ion anisotropies with marked differences in the single-ion electronic parameters of the two iron sites. In this contribution, additional studies are carried out to probe its dynamic magnetic properties. Mossbauer spectra recorded at liquid helium temperatures indicate slow paramagnetic relaxati…
Magnetic Study of a Pentanuclear {Co 2 III Co 3 II } Cluster with a Bent {Co II 3 } Motif
2014
We have synthesised and structurally characterised a new pentanuclear mixed-valent cobalt cluster of formula [CoII3CoIII2(OH)2(piv)6(L)2(H2O)4] (piv = trimethylacetate, H2L = salicylideneanthranillic acid) from reaction of a dinuclear cobalt pivalate precursor with a Schiff base type ligand under mild reaction conditions. The core structure can be conveniently described as two fused Co3–μ3–OH triangles with a strict unique sharing vertex point. A complete picture of the magnetic behaviour of this compound is presented. Through combined use of susceptibility, magnetisation, and EPR data as well as broken-symmetry DFT calculations, we have supported the magnetic data that show weak and anisot…
Semi-empirical simulations of surface relaxation for perovskite titanates
2000
The (100) and (110) surface relaxations are calculated for SrTiO 3 and BaTiO 3 perovskite thin films. By means of a semi-empirical shell model, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are calculated. Surface rumpling and surface-induced dipole moments are calculated for all possible surface terminations. Our results for the (100) surface structure are in good agreement with ab-initio plane-wave pseudopotential calculations and LEED experiments. The surface energy for the Ba-, Sr-, TiO-terminated (110) surfaces is found to be much larger than that for the (100) surface. In contrast, the surface energy for the asymmetric O termination, where outermost…
Relaxation Mechanisms of 5-Azacytosine.
2015
The photophysics and deactivation pathways of the noncanonical 5-azacytosine nucleobase were studied using the CASPT2//CASSCF protocol. One of the most significant differences with respect to the parent molecule cytosine is the presence of a dark (1)(nNπ*) excited state placed energetically below the bright excited state (1)(ππ*) at the Franck-Condon region. The main photoresponse of the system is a presumably efficient radiationless decay back to the original ground state, mediated by two accessible conical intersections involving a population transfer from the (1)(ππ*) and the (1)(nNπ*) states to the ground state. Therefore, a minor contribution of the triplet states in the photophysics o…
Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies
2015
Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20–40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show π-bonding and π*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twist…