Search results for "hyperfine structure"
showing 10 items of 423 documents
Theoretical investigation of paramagnetic group 13 diazabutadiene radicals: insights into the prediction and interpretation of EPR spectroscopy param…
2006
The electronic structures and the spin density distributions of the group 13 1,4-diaza(1,3)butadiene (DAB) radicals [(R-DAB)2M]˙, [(R-DAB)MX2]˙ and {[(R-DAB)MX]2}˙˙ (M = Al, Ga, In; X = F, Cl, Br, I; R = H, Me, tBu, Ph) are studied using density functional theory at both non-relativistic and relativistic levels of theory. The calculations demonstrate that all systems share a qualitatively similar electronic structure and are primarily ligand centred π-radicals. The calculated metal, nitrogen and hydrogen hyperfine couplings are found to be independent of the identity of the R-group and the halogen atom. They are, however, dependent on the geometry and oxidation state of the metal centre. Bo…
Similarity and Specificity of Chlorophyll b Triplet State in Comparison to Chlorophyll a as Revealed by EPR/ENDOR and DFT Calculations
2019
An investigation of the photoexcited triplet state of chlorophyll (Chl) b has been carried out by means of electron nuclear double resonance, both in a frozen organic solvent and in a protein environment provided by the water-soluble chlorophyll protein of Lepidium virginicum. Density functional theory calculations have allowed the complete assignment of the observed hyperfine couplings corresponding to the methine protons and the methyl groups, leading to a complete picture of the spin density distribution of the triplet state in the tetrapyrrole macrocycle. The triplet-state properties of Chl b are found to be similar, in many respects, to those previously reported for Chl a, although som…
Circular dichroism of magnetically induced transitions for D 2 lines of alkali atoms
2018
In this letter we study magnetic circular dichroism in alkali atoms exhibiting asymmetric behaviour of magnetically induced transitions. The magnetic field induces transitions between hyperfine levels of alkali atoms and in the range of magnetic field, the intensities of these transitions experience significant enhancement. We have inferred a general rule applicable for the D 2 lines of all alkali atoms, that is the transition intensity enhancement is around four times larger for the case of than for excitation for , whereas it is several hundreds of thousand times larger in the case of than that for polarization for . This asymmetric behaviour results in circular dichroism. For experimenta…
Iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties
2013
The present work reports on the new soft ferromagnetic Heusler phases Fe${}_{2}$NiGe, Fe${}_{2}$CuGa, and Fe${}_{2}$CuAl, which in previous theoretical studies have been predicted to exist in a tetragonal Heusler structure. Together with the known phases Fe${}_{2}$CoGe and Fe${}_{2}$NiGa these materials have been synthesized and characterized by powder x-ray diffraction, ${}^{57}$Fe M\"ossbauer spectroscopy, superconducting quantum interference device, and energy-dispersive x-ray measurements. In particular M\"ossbauer spectroscopy was used to monitor the degree of local atomic order/disorder and to estimate magnetic moments at the Fe sites from the hyperfine fields. It is shown that in con…
Ultracold atomic Bose and Fermi spinor gases in optical lattices
2006
We investigate magnetic properties of Mott-insulating phases of ultracold Bose and Fermi spinor gases in optical lattices. We consider in particular the F=2 Bose gas, and the F=3/2 and F=5/2 Fermi gases. We derive effective spin Hamiltonians for one and two atoms per site and discuss the possibilities of manipulating the magnetic properties of the system using optical Feshbach resonances. We discuss low temperature quantum phases of a 87Rb gas in the F=2 hyperfine state, as well as possible realizations of high spin Fermi gases with either 6Li or 132Cs atoms in the F=3/2 state, and with 173Yb atoms in the F=5/2 state.
Interacting Rubidium and Caesium Atoms
2007
Binary mixtures of ultracold atoms are of great interest in the research field of quantum optics and are studied by several groups aiming at different applications. This paper works with rubidium and caesium, which are simultaneously stored in a magnetic trap. Species-selective microwave cooling is used on the rubidium groundstate hyperfine transition. Caesium is sympathetically cooled via elastic collisions with rubidium. When cooling down the mixture to temperatures below 1 muK, below 4 muK we observe strong losses of caesium. Analysing the dynamics of sympathetic cooling, lower limit for the modulus of the rubidium-caesium triplet s-wave scattering length is estimated.
A stable oxoverdazyl free radical: Structural and magnetic characterization
2006
Abstract The structure and magnetic properties (susceptibility and ESR) of the stable oxoverdazyl free radical 6-(4-acetamidophenyl)-1,4,5,6-tetrahydro-2,4-dimethyl-1,2,4,5-tetrazin-3(2H)-one are presented. The crystal structure consists of chains of parallel planar molecules running along the b-axis. These chains are formed by dimers with a ring-over-bond overlap and a significant offset between dimers, although with similar inter- and intradimer distances. The susceptibility measurements show that this compound is an S = 1/2 paramagnet with weak antiferromagnetic interactions. The magnetic susceptibility can be very well reproduced with an antiferromagnetic regular chain model with g = 2.…
Structure and Properties of GdAuSn and the GdAuSn/MnAuSn System
2006
The crystal structure of GdAuSn was refined by means of single crystal X-ray diffraction. Band structure calculations based on the structural data confirmed the antiferromagnetic ground state and the metallic behaviour of GdAuSn. 119mSn, 155Gd and 197Au Mossbauer spectroscopic studies were used to verify the values of the hyperfine parameters that were given by the band structure calculations. Band structure calculations of MnAuSn confirmed that this half-Heusler compound belongs to the family of half-metallic ferromagnets. Magnetic susceptibility, conductivity and Mossbauer studies were used to characterize granular material based on the half-Heusler ferromagnet MnAuSn in the antiferromagn…
Nuclear Spins of the IsomersHg191m−185mDetermined by On-Line Quantum-Beat Spectroscopy
1979
The nuclear spins of the very neutron-deficient $^{191m\ensuremath{-}185m}\mathrm{Hg}$ isomers were measured on line at the mass separator ISO LIDE at CERN using pulsed-laser excitation and observation of the time-resolved quantum beats from selected hyperfine-structure states. The spins of these isomers are with $I=\frac{13}{2}$ equal to those of the long-lived isomers $^{199m\ensuremath{-}193m}\mathrm{Hg}$ already known. The persistence of this spin value for eight isomers is explained by the model of rotation-aligned coupling.
Non-Bloch decay of transient nutations in S=1/2 systems: An experimental investigation.
1993
The decay of transient nutations has been experimentally investigated in S=1/2 spin systems at microwave frequency: E' centers in silica and [${\mathrm{AlO}}_{4}$${]}^{0}$ centers in quartz have been studied. We have found that the damping is well described by a single exponential decay function, as expected from a ${\mathit{T}}_{1}$-${\mathit{T}}_{2}$ model (Bloch model). However, the agreement is only qualitative. In fact the measured decay rate \ensuremath{\Gamma} is faster than expected and depends on the driving-field amplitude: it tends to the Bloch value ${\mathrm{\ensuremath{\Gamma}}}_{\mathit{B}}$=1/2${\mathit{T}}_{2}$ in the low-power limit and becomes faster and faster on increas…