Fine Structure Parameters Research Articles

Magnetic anisotropy parameters of matrix-isolated septet 1,3,5-trinitreno-2,4,6-trichlorobenzene

An ESR spectrum of high-symmetry septet 1,3,5-trinitreno-2,4,6-trichlorobenzene generated under photolysis of 1,3,5-triazido-2,4,6-trichlorobenzene in solid argon at 15 K was recorded. Computer simulation revealed that the spectrum corresponds to the septet spin state with the fine structure parameters DS = −0.0957±0.0006 cm−1 and ES = 0±0.0004 cm−1. These values of the magnetic anisotropy parameters DS and ES are in good agreement with the results of UDFT calculations. The spin-spin (DSS) and spin-orbit (DSO) coupling parameters of septet molecules with D3h symmetry are negative and mutually enhance the magnetic anisotropy of these molecules. The contribution of the spin-orbit coupling to the magnetic anisotropy of 1,3,5-trinitreno-2,4,6-trichlorobenzene is higher than 11% due to the presence of three chlorine atoms in the molecule. This suggests the possibility of further strengthening the magnetic properties of septet 1,3,5-trinitrenobenzenes by introducing bromine and iodine atoms into positions 2, 4, and 6 of their benzene rings.

Application of a Continued-Fraction-Based Theory to Line-Profile in Mn-Doped GaN Film

Starting with the Kubo formalism and using the projection operator technique (POT) introduced by Kawabata, the optical quantum transition line-profiles (QTLPs) formula for a Mn-doped wurtzite GaN film was derived as a function of temperature at a frequency of 9.49 GHz (X-band), on the basis of continued fraction representation (CFR) which is a counterpart of the conventional series expansion (CSE). Utilizing this formula we obtained the fine-structure parameter a - F = 9.4 ×10-4 cm-1 and fitting parameter ζ= 4.1. The optical quantum transition half-widths (QTHWs) obtained with the use of these parameters agrees quite well with the existing experimental result in the temperature region T > 20 K. The QTHWs increase with increasing temperature due to the interaction of electrons with optical phonons. Thus, the present technique is considered to be more convenient to explain the resonant system as in the case of other optical transition problems.

Application of a Continued-Fraction-Based Theory to Line-Profile in Mn-Doped GaN Film

Starting with the Kubo formalism and using the projection operator technique (POT) introduced by Kawabata, the optical quantum transition line-profiles (QTLPs) formula for a Mn-doped wurtzite GaN film was derived as a function of temperature at a frequency of 9.49 GHz (X-band), on the basis of continued fraction representation (CFR) which is a counterpart of the conventional series expansion (CSE). Utilizing this formula we obtained the fine-structure parameter a - F = 9.4 ×10-4 cm-1 and fitting parameter ζ= 4.1. The optical quantum transition half-widths (QTHWs) obtained with the use of these parameters agrees quite well with the existing experimental result in the temperature region T > 20 K. The QTHWs increase with increasing temperature due to the interaction of electrons with optical phonons. Thus, the present technique is considered to be more convenient to explain the resonant system as in the case of other optical transition problems.

Phase change of bimetallic PdCo electrocatalysts caused by different heat-treatment temperatures: Effect on oxygen reduction reaction activity

In the present paper, we report the importance of controlling the heat-treatment temperature, the factor that determines the fine structure (core–shell structure or alloy-phase structure) of PdCo bimetallic electrocatalysts. The dependence of the oxygen reduction reaction (ORR) activity of bimetallic PdxCo100−x nanoparticles on the various heat-treatment conditions employed in the preparation process has been investigated. Precise Rietveld refinements of high-resolution powder diffraction data and the fine structure parameters simulated using the extended X-ray absorption fine structure data reveal the following. At a heat-treatment temperature of 300°C, a phase-segregated PdCo core–shell structure (Pd shell on a Co core) is formed, while at higher temperatures (above 500°C), a PdCo alloy phase is formed and the core–shell structure is destroyed. The samples for which the core–shell structure had a high-compressive strain lattice structure with a Pd-rich phase caused a downshift of the d-band center, and eventually, the ORR activity of these samples was better than that of the alloy-phase samples formed by high-temperature heat treatment. Hence, the heat-treatment temperature is the most important factor to be considered in the design of PdCo alloy electrocatalysts.

Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state (II). Population transfer and magnetic field dependence of the spin polarization

The population transfer to the spin-sublevels of the unique quartet (S = 3/2) high-spin state of the strongly exchange-coupled (SC) radical-triplet pair (for example, an Acceptor-Donor-Radical triad (A-D-R)) via a doublet-quartet quantum-mixed (QM) state is theoretically investigated by a stochastic Liouville equation. In this work, we have treated the loss of the quantum coherence (de-coherence) due to the de-phasing during the population transfer and neglected the effect of other de-coherence mechanisms. The dependences on the magnitude of the exchange coupling or the fine-structure parameter of the QM state are investigated. The dependence on the velocity of the population transfer (by the electron transfer or the energy-transfer) from the QM state to the SC quartet state is also clarified. It is revealed that the de-coherence during the population transfer mainly originates from the fine-structure term of the QM state in the doublet-triplet exchange coupled systems. This de-coherence leads to the unique dynamic electron polarization (DEP) on the high-field spin sublevels of the SC state, which is similar to the unique DEP pattern of the photo-excited triplet states of the reaction centers of photosystems I and II. The magnetic field dependence of the population transfer leading to the populations of the spin-sublevels of the SC states is also calculated. The possibility of the control of energy transport, spin transport and information technology by using the QM state is discussed based on these results. The knowledge obtained in this work is useful in the spin dynamics of any doublet-triplet exchange coupled systems.

DFT-BS examination of exchange coupling in chromium(III) dimers containing the μ1,2-squarato bridge

A series of Cr(III) dimers previously reported has had certain structural parameters refined and/or revised using theoretical techniques. These compounds were modeled with isotropic J-couplings that vary between −11.1 and −25.8K. Each dimer contains a bis(μ-hydroxo) bridge. The existence or absence of a bis(μ1,2-squarato) bridge was determined using the density functional theory-broken symmetry approach. The bis(μ1,2-squarato) bridge was determined to be countercomplementary to the bis(μ-hydroxo) bridge. The hydroxo bridges contribute ferromagnetically to the exchange coupling. The results show that triple-ζ basis sets with polarization in conjunction with the B3LYP hybrid DFT method are highly accurate in predicting exchange coupling in these weakly antiferromagnetically coupled Cr(III) systems. The use of the RIJCOSX approximation was also shown to greatly speed up the calculations with a minimal loss in accuracy. Fine structure parameters were also generated using density functional methods, and these parameters matched well with the experimental ones. These results can be used to help verify predicted structures that cannot be crystallized, and they can also aid in designing new compounds tailored to exhibit specific magnetic properties.

EPR spectra and structures of spin-variable iron(III) complexes

The structures of the spin-variable iron(III) complexes Fe(4-OCH3-SalEen)2X and FeL′2X (L′ is oxysalicylidene-N′-ethyl-N-ethylenediamine; X = PF6, NO3, and SCN) were examined from their EPR spectra. The coordination units (CUs) of these complexes are a high-symmetry octahedron with a slight tetrahedral distortion or a low-symmetry pseudooctahedron with considerable tetragonal and orthorhombic distortions. When the complex passes from the high-spin to low-spin state, its CU changes. The energy level splittings caused by various types of distortions were estimated from the EPR data. The distortion of the CU depends on the outer-sphere anion. The magnetic resonance parameters of the complexes were analyzed. The fine structure parameters of the EPR spectra of high-spin complexes (the ground-state term is \(^6 A_{1_g }\)) depend on the CU distortion and the covalent bonding. The spin-orbital coupling makes an appreciable second-order contribution to the expressions for the Zeeman coupling parameters of low-spin complexes (the ground-state term is \(^2 T_{2_g }\)).

Investigating the electronic states of BaOH by V-type double resonance spectroscopy and ab initio calculations: Further evidence of perturbation from the [formula omitted] state

A single band belonging to the A ∼ ′ 2 Δ - X ∼ 2 Σ + band system has been rotationally analyzed for each of the two isotopologues, BaOH and BaOD, using high-resolution V-type optical–optical double resonance spectroscopy. BaOH and BaOD molecules were synthesized in a Broida-type oven. High-resolution spectra were recorded by monitoring the dip in fluorescence of the B ∼ 2 Σ + - X ∼ 2 Σ + transition excited by a single-mode ring dye laser (pump laser), whilst a single-mode Ti:Sapphire laser scanned the corresponding A ∼ ′ 2 Δ - X ∼ 2 Σ + transition. The observed spectra resemble a typical 2 Π - 2 Σ transition, believed to emanate from single or triple quanta of the bending vibration in the A ∼ ′ 2 Δ state. Measured rotational lines have been assigned and rotational and fine structure parameters determined through a combined least-squares fit with the millimeter-wave pure rotational data of the X ∼ 2 Σ + state. Previous analyses of the A ∼ 2 Π - X ∼ 2 Σ + transitions of BaOH and BaOD yielded significantly different spin–orbit coupling constants, which were attributed to possible global and local perturbations arising from vibrationally-excited bands of the A ∼ ′ 2 Δ state. Although the newly observed A ∼ ′ 2 Δ state bands have not been conclusively assigned a specific spin state, the derived Ω-doubling constants show significant 2 Π 1 / 2 character, further indicating strong interactions between the A ∼ 2 Π and A ∼ ′ 2 Δ states of BaOH. To validate these conclusions, ab initio calculations have been carried out to further understand the nature of the BaOH excited states. The D ∼ ′ 2 Σ + , D ∼ 2 Σ + , C ∼ 2 Π , B ∼ 2 Σ + , A ∼ 2 Π , A ∼ ′ 2 Δ and X ∼ 2 Σ + states have been characterized by means of multireference configuration interaction calculations using the MOLPRO software. Calculated vertical term energies show relatively good agreement with existing optical data.

Electronic Structure of a Weakly Antiferromagnetically Coupled MnIIMnIIIModel Relevant to Manganese Proteins: A Combined EPR,55Mn-ENDOR, and DFT Study

An analysis of the electronic structure of the [Mn(II)Mn(III)(μ-OH)-(μ-piv)(2)(Me(3)tacn)(2)](ClO(4))(2) (PivOH) complex is reported. It displays features that include: (i) a ground 1/2 spin state; (ii) a small exchange (J) coupling between the two Mn ions; (iii) a mono-μ-hydroxo bridge, bis-μ-carboxylato motif; and (iv) a strongly coupled, terminally bound N ligand to the Mn(III). All of these features are observed in structural models of the oxygen evolving complex (OEC). Multifrequency electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) measurements were performed on this complex, and the resultant spectra simulated using the Spin Hamiltonian formalism. The strong field dependence of the (55)Mn-ENDOR constrains the (55)Mn hyperfine tensors such that a unique solution for the electronic structure can be deduced. Large hyperfine anisotropy is required to reproduce the EPR/ENDOR spectra for both the Mn(II) and Mn(III) ions. The large effective hyperfine tensor anisotropy of the Mn(II), a d(5) ion which usually exhibits small anisotropy, is interpreted within a formalism in which the fine structure tensor of the Mn(III) ion strongly perturbs the zero-field energy levels of the Mn(II)Mn(III) complex. An estimate of the fine structure parameter (d) for the Mn(III) of -4 cm(-1) was made, by assuming the intrinsic anisotropy of the Mn(II) ion is small. The magnitude of the fine structure and intrinsic (onsite) hyperfine tensor of the Mn(III) is consistent with the known coordination environment of the Mn(III) ion as seen from its crystal structure. Broken symmetry density functional theory (DFT) calculations were performed on the crystal structure geometry. DFT values for both the isotropic and the anisotropic components of the onsite (intrinsic) hyperfine tensors match those inferred from the EPR/ENDOR simulations described above, to within 5%. This study demonstrates that DFT calculations provide reliable estimates for spectroscopic observables of mixed valence Mn complexes, even in the limit where the description of a well isolated S = 1/2 ground state begins to break down.

2D radiative-magnetohydrostatic model of a prominence observed by Hinode, SoHO/SUMER and Meudon/MSDP

Aims. Prominences observed by Hinode show very dynamical and intriguing structures. To understand the mechanisms that are responsible for these moving structures, it is important to know the physical conditions that prevail in fine-structure threads. In the present work we analyse a quiescent prominence with fine structures, which exhibits dynamic behaviour, which was observed in the hydrogen Hα line with Hinode/SOT, Meudon/MSDP and Ondřejov/HSFA2, and simultaneously in hydrogen Lyman lines with SoHO/SUMER during a coordinated campaign. We derive the fine-structure physical parameters of this prominence and also address the questions of the role of the magnetic dips and of the interpretation of the flows.

Effect of plastic deformation on the mechanical properties and the fine-structure parameters of Pb-Ca-Sn alloys

The specific features of structure formation in Pb-Ca-Sn alloys intended for battery current leads are considered. The effect of plastic deformation on the mechanical properties and the fine-structure parameters in Pb-0.1% Ca-0.3% Sn and Pb-0.05% Ca-1.1% Sn alloys is studied. The influence of the initial structure on the mechanical properties and the fine-structure parameters of the alloys is shown, and the variation of the alloy properties under plastic deformation is demonstrated.

Local coordination of Fe3+ in Li[Co0.98Fe0.02]O2 as cathode material for lithium ion batteries—multi-frequency EPR and Monte-Carlo Newman-superposition model analysis

The local coordination of the Fe(3+)-centers in Li[Co(0.98)Fe(0.02)]O(2) cathode materials for lithium-ion batteries has been investigated by means of XRD and multi-frequency EPR spectroscopy. EPR clearly showed the Fe(3+) being in a high-spin state with S = 5/2. The set of spin-Hamiltonian parameters obtained from multi-frequency EPR experiments with Larmor frequencies ranging between 9.8 and 406 GHz was transformed into structural information by means of an expansion to standard Newton-superposition modeling, termed as Monte-Carlo Newman superposition modeling. Based on this analysis, an isovalent incorporation of the Fe(3+)-ions on the Co(3+)-sites, i.e. Fe(x)(Co), has been shown. With that respect, the positive sign of the axial second-order fine-structure interaction parameter B(0)(2) is indicative of an elongated oxygen octahedron, whereas B(0)(2) < 0 points to a compressed octahedron coordinated about the Fe(3+)-center. Furthermore, the results obtained here suggest that the oxygen octahedron about the Fe(3+)-ion is slightly distorted as compared to the CoO(6) octahedron, which in turn may impose mechanical strain to the cathode material.

Calculation of fine structure parameters by semiempirical method from energy intervals between magnetic sublevels

A method is developed for the semiempirical calculation of fine structure parameters from the experimental energy intervals between magnetic sublevels. The calculations are performed using the configuration of neutral carbon as an example. The calculated parameters are used to calculate the 2p2 configuration energy spectrum and the gyromagnetic ratios of the 3P2 and 1D2 levels, as well as the magnetic splitting of triplet levels. The results are compared with available experimental and theoretical data. It is confirmed that the dependence of the energy of magnetic sublevels of np2 configurations on the magnetic induction is parabolic for sublevels with the projections M = 0, ±1 and is linear for sublevels with M = ±2.

Structures and parameters of the EPR spectra of dendrimeric iron(III) complexes

The structures of high-spin iron(III) complexes with poly(propylenimine) dendrimers were examined by EPR spectroscopy. The pseudotetrahedral distortion of the coordination unit (CU) was considered. The fine structure parameters (FSPs) of the EPR spectra were analyzed. A dependence of the FSPs on the CU distortion and the covalent bonding was established. The influence of the axial Cl atoms on FSPs was considered. Splitting of the quartet term caused by the orthorhombic CU distortion with a pseudotetrahedral structure was estimated from the EPR data.

The pure rotational spectrum of TiS (X 3Δ r) at submillimeter wavelengths

The pure rotational spectrum of TiS in its X 3Δ r ground state has been measured using millimeter–wave direct-absorption techniques in the frequency range of 313–425 GHz. This free radical was created by the reaction of titanium vapor, produced in a high-temperature Broida-type oven, with H 2S. Eight to ten rotational transitions were recorded for the main titanium isotopologue, 48TiS, in the v = 0 and v = 1 levels, as well as for the v = 0 state of 46TiS, observed in natural abundance ( 48Ti: 46Ti = 74:8). All three Ω components were observed in almost every recorded transition, with no evidence for lambda-doubling. The data were fit with a Hund’s case(a) Hamiltonian, and rotational, spin–orbit, and spin–spin constants were determined, as well as equilibrium parameters for 48TiS. Relatively few fine structure parameters were needed for the analysis of TiS ( A, A D, and λ), unlike other 3d metal species. The rotational pattern of the three fine structure components suggests the presence of a nearby excited 1Δ state, lying ∼3000 cm −1 higher in energy. From the equilibrium parameters, the dissociation energy for TiS was estimated to be ∼5.1 eV, in reasonable agreement with past thermochemical data.

Fe3+ Ions Acting as Probes and Agents in Aggregation Processes and Solid‐State Reactions in AlO(OH)/Al2O3 Matrices

The fate of doped iron species during various mechanically and thermally initiated redox reactions and aggregation processes in crystalline and amorphous AlO(OH) or Al2O3 matrices was investigated. The amorphization of the matrix was performed by chemical (i.e., via sol–gel processes) or mechanochemical treatment (high‐energy ball milling). Thermal analysis, coupled with mass spectrometry (TA‐MS), Mössbauer spectroscopy, and electron spin resonance (ESR), was used. The TA under various gas atmospheres allowed preparing samples under a controlled temperature regime, together with a controlled gas influence. Both the effect of mechanical activation and the influence of the iron doping could be followed macroscopically via the down‐shift of the peak temperature of the corundum formation. The ESR data characterize the Fe3+ ions and their interaction with the magnetic surrounding based on the fine structure parameters. The Mössbauer data allowed the characterization of the Fe(0), Fe2+, and Fe3+ species, together with providing information about their coordinative surrounding. Both methods provided general complementary spectroscopical information. Unexpectedly, (FeOx)n and (FexAl1−x)2O3 aggregates could also be detected in the range of low Fe concentrations. It was demonstrated that even in the low‐level doped systems [(FexAl1−x)2O3 with x≥0.01], all the essential spectroscopic phenomena occur. At higher Fe concentrations, they were discovered to be caused by magnetic and spin exchange interactions as well as by solid‐state reactions during and after the mechanical activation.

EPR study of chromium centres formed in hexagonal RbMgF3 and RbZnF3 single crystals

AbstractEPR measurements have been made on single crystals of RbMgF3 doped only with chromium or codoped with chromium and lithium. Three kinds of trigonally symmetric Cr3+ spectra were observed. Strong spectrum observed from codoped RbMgF3 is ascribed to Cr3+–Li+ pair centre. Other two centres are identified by considering the signs of the fine structure parameters $b_2^0$. Weak spectrum observed from RbMgF3 doped only with chromium is ascribed to a simply‐substituting Cr3+ ion at the MgII site in the face‐sharing Mg2F9 unit. The spectrum observed after X‐ray irradiation for the above crystal is ascribed to a simply‐substituting Cr3+ ion at the MgI site in the single octahedron unit. Similar Cr3+ centres are identified for hexagonal‐RbZnF3 codoped with chromium and lithium. An empirical rule for the sign and magnitude of the $b_2^0$ parameter among the Cr3+ centres in the hexagonal‐BaTiO3 type fluorides is presented. Site preference substitution by trivalent chromium ion in RbMgF3 was found.

A multifrequency EPR study of Fe 2+ and Mn 2+ ions in a ZnSiF 6·6H 2O single crystal at liquid-helium temperatures

A liquid-helium temperature study of Fe 2+ and Mn 2+ ions has been carried out on a single crystal of Fe 2+-doped ZnSiF 6·6H 2O at 5–35 K at 170, 222.4 and 333.2 GHz. The spectra are found to be an overlap of two magnetically inequivalent Fe 2+ ions, as well as that of an Mn 2+ ion. From the simulation of the EPR line positions for the Fe 2+ (d 6, S = 2) ion the spin-Hamiltonian parameters were estimated for the two inequivalent Fe 2+ ions at the various temperatures. From the relative intensities of lines the absolute sign of the fine-structure parameters have been estimated. In addition, the fine-structure and hyperfine-structure spin-Hamiltonian parameters for the Mn 2+ ion, present as impurity at interstitial sites, were estimated from the hyperfine allowed and forbidden line positions. The particular virtues of such a single-crystal study vs. that on powders are noted.

High-resolution laser spectroscopy of the [formula omitted] transition of MgC 4H

The 0 0 0 band of the A ˜ 2 Π - X ˜ 2 Σ + transition of MgC 4H has been recorded at high resolution using laser-induced fluorescence. The molecules were produced using an ablation source by the reaction of magnesium and ∼10% acetylene seeded in helium. The rotationally-resolved high-resolution data were fitted to obtain rotational and fine structure parameters for both states. The centrifugal distortion, upper state Λ-doubling and ground state spin-rotation splitting parameters were all found to be negligible and the reasons for this are investigated and discussed. The 3 0 1 band heads of the A ˜ 2 Π - X ˜ 2 Σ + transition of MgC 6H were obtained but the rotational structure was not resolved.

Hyperfine structure and Zeeman tuning of theA Π2−X Σ2+(0,0)band system of the odd isotopologue of strontium monofluorideS87rF

The low-rotational lines of the $A\text{ }^{2}\ensuremath{\Pi}\text{\ensuremath{-}}X\text{ }{^{2}\ensuremath{\Sigma}}^{+}(0,0)$ band system of the odd isotopologue of strontium monofluoride, $^{87}\text{S}\text{rF}$, were recorded and analyzed. The $^{87}\text{S}\text{r}(I=9/2)$ magnetic hyperfine interaction is significant only in the $|\ensuremath{\Omega}|=1/2$ spin-orbit component of the $A\text{ }^{2}\ensuremath{\Pi}$ state. Optical transitions appropriate for monitoring ultracold samples of $^{87}\text{S}\text{rF}$ are identified. The determined fine-structure parameters were used to predict the anisotropic magnetic $g$ factor, ${g}_{l}$, for the $X\text{ }{^{2}\ensuremath{\Sigma}}^{+}(v=0)$ state. The $g$ factors were used to predict the magnetic tuning of the $N=0$ $(+\text{parity})$ and $N=1$ $(\ensuremath{-}\text{parity})$ levels of the $X\text{ }{^{2}\ensuremath{\Sigma}}^{+}(v=0)$ state. A comparison to spectroscopic parameters for the $^{88}\text{S}\text{rF}$ isotopologue is given.