Angular variation of electron paramagnetic resonance spectrum: simulation of a polycrystalline EPR spectrum

A procedure based on homotopy, involving a quick calculation of EPR line positions for various orientations of the external magnetic field by the method of least-squares fitting and Taylor-series expansion, using a known line position at an infinitesimally close orientation of the external magnetic field as the initial value, by using the eigenvectors and eigenvalues of the spin-Hamiltonian matrix in single crystals, has been exploited to simulate a polycrystalline EPR spectrum. This requires rigorous calculations of intensities of resonant lines, along with their positions. Specifically, details are given of the numerical techniques involving time-efficient matrix diagonalization to obtain the eigenvalues and eigenvectors required to calculate positions and intensities of EPR lines by the method of least-squares fitting. Finally, the procedure of how to simulate a polycrystalline EPR spectrum is outlined, the required steps are listed, and illustrative examples are given.     

Temperature dependence of EPR linewidth in one-dimensional magnets: A quasi-classical approach

An analytical expression for the EPR linewidth of an exchange-coupled 1/2-spin chain originating from uniform Dzyaloshinskii-Moriya interaction is derived using a quasi-classical approach. The expression successfully reproduces the results obtained by numerical quantum mechanical calculations based on Green’s function method at T > 2J/k _B.     

Optical spectra and spin-Hamiltonian parameters of trivalent ytterbium in lead tungstate

By using crystal-field theory, the optical spectra and spin-Hamiltonian parameters (abbr. SH parameters, i.e. the anisotropic g factors g _∥, g _⊥, and hyperfine structure constants A _∥, A _⊥) of ¹⁷¹Yb^3 + and ¹⁷³Yb^3 + isotopes in the tetragonal PbWO₄ are calculated. The theoretical results agree well with the experimental values. The crystal-field parameters and the signs of the hyperfine structure constants for both ¹⁷¹Yb^3 + and ¹⁷³Yb^3 + isotopes are determined. The validities of the theoretical results are discussed.     

The EPR spectrum of the OD radical: A determination of molecular parameters for the ground state

The gas-phase EPR spectrum of the OD radical in its ground state was recorded at 8970 MHz. Transitions were observed for levels in both spin components of the X²Π state. The measurements were combined with data from the molecular beam electric resonance spectrum and from the far-infrared spectrum to determine a set of molecular parameters for OD in the v = 0 level of the ²Π state. These parameters are used in conjunction with the corresponding ones for OH to determine values for the spin-rotation constant γ and the correction to the spin-orbit coupling parameter A_D for the level v = 0. A less reliable determination is made of the values for the spin-orbit coupling parameters A_e and α_A. The set of molecular parameters is also used to calculate the frequencies and line strengths of transitions between low-lying levels in the far infrared in order to aid the identification of OD in astrophysical sources.     

Effect of own radiation on the linewidth and absorption spectrum of a probe field

The absorption spectrum of a probe field upon self-saturation on the transition between levels with angular momenta equal to 1/2 is considered. A new class of nonlinear spectroscopic phenomena caused by the nonlinearity (with respect to the density matrix) of the radiative relaxation matrix is predicted. The relative role of the own spontaneous radiation in the broadening of the combining levels and the line, as well as the dependence of the absorption on the polarization of the probe field, is elucidated.     

晶体材料中3d2态离子自旋哈密顿参量的微观起源

采用了中间场耦合图像，考虑了以前研究中被忽略的SS (spin-spin)磁相互作用以及SOO (spin-other-orbit)磁相互作用，利用完全对角化方法，研究了3d₂态离子在三角对称 (C_3v, D₃, D_3d)晶体中自旋哈密顿(SH)参量的微观起源.发现自旋哈密顿参量 (包括零场分裂参量D和g因子g∥,g⊥)来自四种耦合机理：（1）SO (spin-orbit)耦合机理; (2) SS耦合机理；（3）SOO 关键词： 自旋哈密顿参量 2态离子')" href="#">3d₂态离子 三角对称晶场 SS与SOO作用 SO-SS-SOO联合作用机理     

A rigorous description of the energy spectrum of the ammonia dimer. II. Taking into account the inversional motion

Using the group chain methods, a rigorous algebraic model for describing the energy spectrum of the ammonia dimer (NH₃)₂ is constructed with an allowance for both the most important torsional and exchange nonrigid motions and the inversional nonrigid motion also taken into account. The model is rigorous in the sense that its correctness is limited only by the correctness of the chosen symmetry of internal dynamics of the dimer.     

A rigorous description of the energy spectrum of the ammonia dimer. I. Taking into account the torsional and exchange motions

Using the methods of a symmetry group chain, a rigorous algebraic model for describing the energy spectrum of the ammonia dimer (NH₃)₂ is constructed with the torsional and exchange nonrigid motions taken into account. The model is rigorous in the sense that its correctness is limited only by the correctness of the chosen symmetry of internal dynamics of the dimer.     

Effect of a weak dimer-dimer interaction on the EPR line shape of polycrystalline samples

The spectroscopic manifestations of a weak interaction between dimers in the EPR spectra of polycrystalline samples are analyzed. It is shown that, under specific conditions, the weak interaction between dimers can be responsible for the additional lines in the EPR spectrum. The appearance of these features is associated with the collapse of the spectral lines in orientations satisfying the condition of exchange narrowing for the components of the fine structure in the spectrum of the dimer.     

Measurement of the microwave tensor susceptibility and the effective linewidth of polycrystalline ferrite with a rotating DC magnetic field

Nuclear magnetic resonance measurements of the quadrupolar splittings at rare-earth sites in a series of rare-earth/Fe₂, A1₂ and Zn ordered intermetallics are reported. It is demonstrated that under certain conditions these measurements may be used to determine the value of <J_zfor the 4f electrons with relatively high precision. For the rare-earth/Fe₂ compounds studied we find moment reductions of the order of 4% below the free ion values. These results are consistent with those of polarised neutron studies.     

Investigations of the optical spectra and spin-Hamiltonian parameters for the rhombic Yb centers in garnets

Two complete diagonalization (of energy matrix) methods (CDM-I and CDM-II) are used to calculate the six optical spectral band positions and nine spin-Hamiltonian (SH) parameters (g factors g_i and hyperfine structure constants ¹⁷¹A_i, ¹⁷³A_i, where i=x, y, z) for Yb³⁺ ions in the rhombic dodecahedral sites of garnets Y₃Al₅O₁₂, Lu₃Al₅O₁₂ and Y₃Ga₅O₁₂. In CDM-I, the Hamiltonian concerning energy matrix does not contain the Zeeman and hyperfine interaction terms, whereas in CDM-II, it does. So, in CDM-I, the SH parameters are obtained by first-order perturbation method or the equivalence between SH and Zeeman term (or hyperfine interaction term) and in CDM-II, the SH parameters and optical spectral band positions are calculated together. The results obtained from both methods are not only close to each other, but also in reasonable agreement with the observed values. So the second-order perturbation formulas of SH parameters developed recently are incorrect and unnecessary.     

On rigorous mathematical definitions of correlation dimension and generalized spectrum for dimensions

We consider different definitions of the correlation dimension and find some relationships between them and other characteristics of dimension type such as Hausdorff dimension, box dimension, etc. We also introduce different ways to define and study the generalized spectrum for dimensions—a one-parameter family of characteristics of dimension type.     

Sub-natural linewidth of the probe absorption spectrum in a cold Cs atom molecule system

We theoretically analysed the linewidth of the probe absorption spectrum in a cold Cs atom--molecule system. The tunnelling coupling between the two excited molecular states, especially for the Cs atom--molecule system, plays an important role in obtaining the sub-natural linewidth of the probe absorption spectrum. For example, when the tunnelling couple strength fulfils \sigma _12=10γ _ab₁, the linewidth is only about 0.66~MHz. Moreover, since the linewidth of interest is dominated by the tunnelling coupling, the absorption peak becomes very narrow even in the case of large pump laser intensities.     

Estimation of mean and median pO2 values for a composite EPR spectrum

Electron paramagnetic resonance (EPR)-based oximetry is capable of quantifying oxygen content in samples. However, for a heterogeneous environment with multiple pO2 values, peak-to-peak linewidth of the composite EPR lineshape does not provide a reliable estimate of the overall pO2 in the sample. The estimate, depending on the heterogeneity, can be severely biased towards narrow components. To address this issue, we suggest a postprocessing method to recover the linewidth histogram which can be used in estimating meaningful parameters, such as the mean and median pO2 values. This information, although not as comprehensive as obtained by EPR spectral-spatial imaging, goes beyond what can be generally achieved with conventional EPR spectroscopy. Substantially shorter acquisition times, in comparison to EPR imaging, may prompt its use in clinically relevant models. For validation, simulation and EPR experiment data are presented.     

Enhanced EPR sensitivity from a ferroelectric cavity insert.

We report the development of a simple ferroelectric cavity insert that increases the electron paramagnetic resonance (EPR) sensitivity by an order of magnitude when a sample is placed within it. The insert is a hollow cylinder (length 4.8 mm, outside diameter 1.7 mm, inside diameter 0.6 mm) made from a single crystal of KTaO(3), which has a dielectric constant of 230 at X-band (9.5 GHz). Its outside dimensions were chosen to produce a resonant frequency in the X-band range, based on electromagnetic field modeling calculations. The insert increases the microwave magnetic field (H(1)) at the center of the insert by a factor of 7.4 when placed in an X-band TM(110) cavity. This increases the EPR signal for a small (volume 0.13 microL) unsaturated nitroxide spin label sample by a factor of 64 at constant microwave power, and by a factor of 9.8 at constant H(1). The insert does not significantly affect the cavity quality factor Q, indicating that this device simply redistributes the microwave fields within the cavity, focusing H(1) onto the sample inside the insert, thus increasing the filling factor. A similar signal enhancement is obtained in the TM(110) and TE(102) cavities, and when the insert is oriented either vertically (parallel to the microwave field) or horizontally (parallel to the DC magnetic field) in the TM(110) cavity. This order-of-magnitude sensitivity enhancement allows EPR spectroscopy to be performed in conventional high-Q cavities on small EPR samples previously only measurable in loop-gap or dielectric resonators. This is of particular importance for small samples of spin-labeled biomolecules.