Hyperfine Constants Research Articles

EPR Spectrum Analysis of DPPH and MnCl2

This paper presents the findings of electron paramagnetic resonance (EPR) spectroscopy experiments conducted on two different samples: 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Manganese Chloride (MnCl2) dissolved in H2O. The experiments were conducted at Dr. D. Petasis EPR lab located in Allegheny College, Meadville, PA, USA. A Varian X-Band spectrometer was utilized for the analysis of the EPR absorption spectra. The primary objective was to determine the g-values and hyperfine structure of the two samples, which can be crucial in characterizing their electronic properties. The g-values obtained for both DPPH and MnCl2 were found to be remarkably close to the theoretically calculated values, suggesting the high accuracy and success of the experiments. This agreement validates the reliability of the EPR measurements and demonstrates the precision of the instruments and experimental procedures employed. For the MnCl2 sample, a hyperfine structure with 6 visible EPR lines was observed. By analyzing the number of EPR lines, the nuclear spin of the Mn(II) ion was determined to be I = 5/2, consistent with the expected value for Mn(II). The hyperfine constant (A) was also calculated from the field position differences between adjacent lines, providing further insights into the sample's magnetic properties. Comparisons were made between the obtained g-values and hyperfine constant with the expected values for Mn(II) in the literature, confirming the accuracy of the measurements and reinforcing the credibility of the experimental data. Overall, the EPR spectroscopy experiments conducted on DPPH and MnCl2 in H2O have provided valuable information about the electronic and magnetic properties of these paramagnetic materials. The results demonstrate the effectiveness of EPR spectroscopy as a powerful experimental technique for investigating various bio-chemical samples and understanding the effects of solvents on the EPR spectra of compounds. The close agreement between the experimental and theoretical values for the g-factors and hyperfine constants reinforces the reliability of the data obtained from the EPR experiments.

Absolute Frequency Measurements of the D Lines in ^{9}Be^{+} Using a Single Trapped Ion.

Optical frequencies of the D line transitions in ^{9}Be^{+} were measured with a relative uncertainty of Δν/ν=5×10^{-11}. The results represent the highest accuracy achieved on a broad electric dipole-allowed (E1) transition in a trapped ion experiment to date, enabled in part by detailed consideration of photon recoil and quantum interference. Measurements were made on a single laser-cooled ion stored in a radio frequency Paul trap, using a spectroscopy laser stabilized to an optical frequency comb and referenced to UTC (NIST). The uncertainties in the D_{1} and D_{2} lines have been reduced by a factor of 10 and 30, respectively, compared to previous work. We have extracted the ^{2}P fine structure splitting, Δν_{fs}=197 064.54(7) MHz, and the ^{2}P_{1/2} hyperfine constant, A_{P_{1/2}}=-117.92(4) MHz.

EPR Sensing of a Cation Species by Aza-Crown Ethers Incorporating a Persistent Nitroxidic Radical Unit.

New nitroxides based on aza-crown ethers were prepared and employed as selective sensors for the detection of inorganic and organic cations by EPR analysis of the corresponding host-guest complexes. The nitroxide unit behaves as a sensitive probe for a number of alkali and alkaline earth metal cations affording EPR spectra differing in the value of nitrogen hyperfine constants and in the appearance of splitted signals due to the non-zero nuclear spin of some metal cation upon complexation. Owing to the remarkable EPR spectral differences between the host and the corresponding cation complex the new macrocycles are likely to act as multitasking tools to recognize several cationic species. EPR behaviour of the larger nitroxide azacrown 1⋅ when acting as a wheel in a radical synthetic bistable [2]rotaxane containing both secondary dialkylammonium and 1,2-bis(pyridinium) molecular stations, was also investigated. Reversible movements of the macrocycle between the two recognition sites in the rotaxane were promptly revealed by EPR, which shows significant changes either in nitrogen coupling constant values (aN ) or in the spectral shape in the two rotaxane co-conformations.

Molecular Structure Related to an S = 5/2 High-Spin S2 State Manganese Cluster of Photosystem II Investigated by Q-Band Pulse EPR Spectroscopy.

The high-spin S2 state of the photosynthetic oxygen-evolving cluster Mn4CaO5, corresponding to the g = 4.1 signal for X-band electron paramagnetic resonance (EPR), was investigated using Q-band pulsed EPR, which detected a main peak at g = 3.10 and satellite peaks at 5.25, 4.55, and 2.80. We evaluated the spin state as the zero-field splitting of D = 0.465 cm-1 and E/D = 0.245 with S = 5/2. The temperature dependence of the T1 relaxation time revealed that the excited-state energy was 28.7 cm-1 higher than that of the S = 5/2 ground state. By comparing present quantum mechanical (QM) calculation models, a closed-cubane structure with the protonation state of two oxygens, W1 (= OH-) and W2 (= H2O), was the most probable structure for the S = 5/2 state. The three-pulse electron spin-echo envelope modulation (ESEEM) detected the nuclear signal, which was assigned to nitrogen as His332 ligated to the Mn1 ion. The obtained hyperfine constant for the nitrogen signal was significantly reduced from that in the S = 1/2 low-spin state. These results indicate that the S = 5/2 spin state arises from the closed-cubane structure.

Rotation dependence of v′ = 44 excited-state hyperfine constants obtained via precise measurements of the hyperfine structures of 127I2 lines near 514 nm

Rotation dependence of v′ = 44 excited-state hyperfine constants obtained via precise measurements of the hyperfine structures of 127I2 lines near 514 nm

Phosphorus fluoride exchange: Multidimensional catalytic click chemistry from phosphorus connective hubs

Phosphorus Fluoride Exchange (PFEx) represents a cutting-edge advancement in catalytic click-reaction technology. Drawing inspiration from Nature's phosphate connectors, PFEx facilitates the reliable coupling of P(V)-F loaded hubs with aryl alcohols, alkyl alcohols, and amines to produce stable, multidimensional P(V)-O and P(V)-N linked products. The rate of P-F exchange is significantly enhanced by Lewis amine base catalysis, such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). PFEx substrates containing multiple P-F bonds are capable of selective, serial exchange reactions via judicious catalyst selection. In fewer than four synthetic steps, controlled projections can be deliberately incorporated along three of the four tetrahedral axes departing from the P(V) central hub, thus taking full advantage of the potential for generating three-dimensional diversity. Furthermore, late-stage functionalization of drugs and drug fragments can be achieved with the polyvalent PFEx hub, hexafluorocyclotriphosphazene (HFP), as has been demonstrated in prior research.

Investigation of the 6s6p3P2-6s7s3S1 transition of ytterbium atoms with modulation-transfer spectroscopy

We perform the precise measurement of the 6s6p3P2-6s7s3S1 transition frequencies of the neutral ytterbium (Yb) atoms by using the modulation transfer spectroscopy. High-resolution dispersive signals of all isotopes except low-abundance 168Yb (F = 2-F = 1) and 171Yb (F = 5/2-F = 3/2) are obtained. The frequencies of locked laser are measured using an optical comb, and the obtained results are traced to the absolute transition frequency of the 171Yb 1S0-3P0 clock. We measure the isotope shifts relative to 174Yb and evaluate the systematic shifts. The absolute frequency of the 6s6p3P2-6s7s3S1 transition in 174Yb is determined to be 389260605.8 ± 3.2 MHz, which has a huge deviation from the existing data in the studies. Based on the obtained transition frequencies, we calculate the hyperfine constants of the 3P2 and 3S1 states. This research will provide valuable data for the ytterbium-related experiments and improve the reported transition frequencies with higher precision.

A Simulation Independent Analysis of Single- and Multi-Component cw ESR Spectra.

The accurate analysis of continuous-wave electron spin resonance (cw ESR) spectra of biological or organic free-radicals and paramagnetic metal complexes is key to understanding their structure-function relationships and electrochemical properties. The current methods of analysis based on simulations often fail to extract the spectral information accurately. In addition, such analyses are highly sensitive to spectral resolution and artifacts, users' defined input parameters and spectral complexity. We introduce a simulation-independent spectral analysis approach that enables broader application of ESR. We use a wavelet packet transform-based method for extracting g values and hyperfine (A) constants directly from cw ESR spectra. We show that our method overcomes the challenges associated with simulation-based methods for analyzing poorly/partially resolved and unresolved spectra, which is common in most cases. The accuracy and consistency of the method are demonstrated on a series of experimental spectra of organic radicals and copper-nitrogen complexes. We showed that for a two-component system, the method identifies their individual spectral features even at a relative concentration of 5% for the minor component.

Frequency measurement of 6s6p 3P0,2−6s7s 3S1 transitions in ultracold 171Yb atoms referenced to local optical clock

We experimentally determine the absolute frequencies and hyperfine splittings of the 6s6p3P0,2 − 6s7s3S1 transitions of ultracold 171Yb atoms in an optical lattice. A frequency comb referenced to an ultrastable optical cavity is used to measure the electric-dipole transition frequencies. With the normalized shelving detection technique, about 12 MHz and 10 MHz linewidth of atomic spectra are obtained, respectively, which is some greater than the natural linewidth of 1.5 MHz and 5.9 MHz and is limited by the broadening from the probe and lattice light. By reference to our 171Yb 6 s2 1S0 − 6s6p3P0 clock, the absolute frequencies are found to be 461861338.03 (0.21) MHz and 461871596.07 (0.31) MHz for the 6s6p3P0 − 6s7s3S1 (F = 1/2 and F = 3/2) transitions, which are more accurate than the previous measurement by one order of magnitude. For the 6s6p3P2 (F = 3/2 and F = 5/2) − 6s7s3S1 (F = 1/2 and F = 3/2) transitions, the measured frequencies are 389257019.71 (0.65) MHz, 389267277.10 (0.37) MHz and 389260569.95 (0.89) MHz, respectively, which are the first measurements to our knowledge. Furthermore, the hyperfine constants for the 6s6p3P2 and 6s7s3S1 states are determined to be 2682.86(0.38) MHz and 6838.69(0.25) MHz, both of which agree well with other recent experimental results.

Measurement of hyperfine constants and the isotope shift of rubidium 5P1/2 excited-state using saturated absorption spectroscopy

The Saturated Absorption Spectroscopy (SAS) was performed to measure the hyperfine constants of rubidium 5P1/2 excited state using an external-cavity diode laser (ECDL) operating at 795 nm. We report our measurements for the magnetic dipole coupling constants 120.79(29) and 407.75(57) for 85 Rb and 87 Rb respectively. Our measurement of the 85 Rb hyperfine constant shows a good agreement with previous results and our measurement of the 87 Rb hyperfine constant resolves the discrepancy of results that exists in the literature.

The Electronic Structures and Energies of the Lowest Excited States of the Ns0, Ns+, Ns− and Ns-H Defects in Diamond

This paper reports the energies and charge and spin distributions of the mono-substituted N defects, N0s, N+s, N-s and Ns-H in diamonds from direct Δ-SCF calculations based on Gaussian orbitals within the B3LYP function. These predict that (i) Ns0, Ns+ and Ns- all absorb in the region of the strong optical absorption at 270 nm (4.59 eV) reported by Khan et al., with the individual contributions dependent on the experimental conditions; (ii) Ns-H, or some other impurity, is responsible for the weak optical peak at 360 nm (3.44 eV); and that Ns+ is the source of the 520 nm (2.38 eV) absorption. All excitations below the absorption edge of the diamond host are predicted to be excitonic, with substantial re-distributions of charge and spin. The present calculations support the suggestion by Jones et al. that Ns+ contributes to, and in the absence of Ns0 is responsible for, the 4.59 eV optical absorption in N-doped diamonds. The semi-conductivity of the N-doped diamond is predicted to rise from a spin-flip thermal excitation of a CN hybrid orbital of the donor band resulting from multiple in-elastic phonon scattering. Calculations of the self-trapped exciton in the vicinity of Ns0 indicate that it is essentially a local defect consisting of an N and four nn C atoms, and that beyond these the host lattice is essential a pristine diamond as predicted by Ferrari et al. from the calculated EPR hyperfine constants.

Difference in Structure and Electronic Properties of Oxygen Vacancies in α-Quartz and α-Cristobalite Phases of SiO2

α-cristobalite (α-C) is a polymorph of silica, mainly found in space exploration and geochemistry research. Due to similar densities, α-C is often used as a proxy for amorphous SiO2, particularly in computer simulations of SiO2 surfaces and interfaces. However, little is known about the properties of α-C and its basic oxygen defects. Using density functional theory (DFT) simulations we provide a comprehensive report on the properties of perfect structure and oxygen vacancies in α-C. The calculated properties of α-C are compared with those of the better-characterized α-quartz (α-Q). Our results demonstrated that the positively charged O vacancy in α-C is most stable in the dimer configuration, in contrast to α-Q, which favors the puckered configuration. A back-projected configuration was also predicted in both polymorphs. We calculated the optical transition energies and isotropic hyperfine constants for O vacancies in both α-Q and α-C, and compared our findings with the results of previous studies and experiments. This work, thus, offers one of the first in-depth investigations of the properties of oxygen vacancies in α-C.

Frequency references based on molecular iodine for the study of Yb atoms using the 1S0 - 3P1 intercombination transition at 556 nm.

We used precision spectroscopy to analyze the R(53)24-1, P(49)24-1, and R(95)25-1 lines of molecular iodine (127I2) to establish optical frequency references for the laser cooling of Yb atoms using the 1S0 - 3P1 intercombination transition at 556 nm. A laser frequency instability of < 2 × 10-12 (for 0.01 s < τ < 3000 s, τ is the average time of the measurement) was attained using the observed Doppler-free hyperfine transitions of the iodine lines. The absolute frequencies of the observed 63 hyperfine transitions were determined with an uncertainty of 7 kHz (fractional uncertainty of 1.3 × 10-11). Highly accurate hyperfine constants were determined by fitting the measured hyperfine splittings to a four-term Hamiltonian that includes the electric quadrupole, spin-rotation, tensor spin-spin, and scalar spin-spin interactions with an uncertainty of approximately 1 kHz. The observed hyperfine transitions of molecular iodine provide new frequency references for research using atomic Yb, because these transitions are close to the intercombination transition of Yb at 556 nm.

Study of Tricalcium Phosphate Ceramics Doped with Gadolinium Ions with Various EPR Techniques

Tricalcium phosphate (TCP)-based materials, such as β-Ca3(PO4)2 doped with rare earth ions (RE), have shown applications as biomaterials, lighting emitting materials, scintillating materials, in vivo imaging probes, and thermoluminescent dosimeters. Their properties are found to be dependent on the distribution of RE3+ on Ca2+ sites that can be controlled by pulsed electron paramagnetic resonance (EPR) and electron spin echo envelop modulation (ESEEM) experiments. The main spectroscopic parameters (spin Hamiltonian values) of Gd3+ and nitrogen impurity centers are quantitatively determined (g-factor, the fine structure parameters D and E, the hyperfine constants A) as well as dynamic characteristics: spin–lattice T1 and spin–spin T2 relaxation times. Based on the analysis of the EPR datasets, the interatomic distance between Gd3+ and 31P was estimated in the dipole–dipole approximation. Two structurally nonequivalent Gd3+ positions in the β-TCP structure have been identified. The obtained valuable results demonstrate applicability of modern EPR techniques to characterize Gd-TCP systems despite the powder structure of the material and high electron spin S = 7/2 of Gd3+ ions.

Stability and electronic structure of NV centers at dislocation cores in diamond

We present a density functional theory analysis of the negatively charged nitrogen-vacancy (NV) defect complex located at or close to the core of 30$^\circ$ and 90$^\circ$ partial glide dislocations in diamond. Formation energies, electronic densities of states, structural deformations, hyperfine structure and zero-field splitting parameters of NV centers in such structurally distorted environments are analyzed. The formation energies of the NV centers are up to 3 eV lower at the dislocation cores compared to the bulk values of crystalline diamond. We found that the lowest energy configuration of the NV center at the core of a 30$^\circ$ partial glide dislocation is realized when the axis of the NV center is oriented parallel to the dislocation line. This special configuration has a stable triplet ground state. Its hyperfine constants and zero field splitting parameters deviate by only 3% from values of the bulk NV center. Hence, this is an interesting candidate for a self-assembly of a linear array of NV centers along the dislocation line.

Survey of Hyperfine Structure Measurements in Alkali Atoms

The spectroscopic hyperfine constants for all the alkali atoms are reported. For atoms from lithium to cesium, only the long lived atomic isotopes are examined. For francium, the measured data for nuclear ground states of all available isotopes are listed. All results obtained since the beginning of laser investigations are presented, while for previous works the data of Arimondo et al. [Rev. Mod. Phys. 49, 31 (1977)] are recalled. Global analyses based on the scaling laws and the hyperfine anomalies are performed.

Laboratory and Astronomical Detection of the SiP Radical (X2Π i ): More Circumstellar Phosphorus

The millimeter-wave spectrum of the SiP radical (X2Πi) has been measured in the laboratory for the first time using direct-absorption methods. SiP was created by the reaction of phosphorus vapor and SiH4 in argon in an AC discharge. Fifteen rotational transitions (J + 1 ← J) were measured for SiP in the Ω = 3/2 ladder in the frequency range 151–533 GHz, and rotational, lambda doubling, and phosphorus hyperfine constants determined. Based on the laboratory measurements, SiP was detected in the circumstellar shell of IRC+10216, using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory at 1 mm and 2 mm, respectively. Eight transitions of SiP were searched: four were completely obscured by stronger features, two were uncontaminated (J = 13.5 → 12.5 and 16.5 → 15.5), and two were partially blended with other lines (J = 8.5 → 7.5 and 17.5 → 16.5). The SiP line profiles were broader than expected for IRC+10216, consistent with the hyperfine splitting. From non-LTE radiative transfer modeling, SiP was found to have a shell distribution with a radius ∼300 R *, and an abundance, relative to H2, of f ∼ 2 × 10−9. From additional modeling, abundances of 7 × 10−9 and 9 × 10−10 were determined for CP and PN, respectively, both located in shells at 550–650 R *. SiP may be formed from grain destruction, which liberates both phosphorus and silicon into the gas phase, and then is channeled into other P-bearing molecules such as PN and CP.

Precise determination of the low-energy electronuclear Hamiltonian of LiY1−xHoxF4

We use complementary optical spectroscopy methods to directly measure the lowest crystal-field energies of the rare-earth quantum magnet LiY$_{1-x}$Ho$_{x}$F$_{4}$, including their hyperfine splittings, with more than 10 times higher resolution than previous work. We are able to observe energy level splittings due to the $^6\mathrm{Li}$ and $^7\mathrm{Li}$ isotopes, as well as non-equidistantly spaced hyperfine transitions originating from dipolar and quadrupolar hyperfine interactions. We provide refined crystal field parameters and extract the dipolar and quadrupolar hyperfine constants ${A_J=0.02703\pm0.00003}$ $\textrm{cm}^{-1}$ and ${B= 0.04 \pm0.01}$ $\textrm{cm}^{-1}$, respectively. Thereupon we determine all crystal-field energy levels and magnetic moments of the $^5I_8$ ground state manifold, including the (non-linear) hyperfine corrections. The latter match the measurement-based estimates. The scale of the non-linear hyperfine corrections sets an upper bound for the inhomogeneous line widths that would still allow for unique addressing of a selected hyperfine transition. e.g. for quantum information applications. Additionally, we establish the far-infrared, low-temperature refractive index of LiY$_{1-x}$Ho$_{x}$F$_{4}$.

Effect of Mn2+ ions on spectroscopic and electrical properties of lithium strontium borate glasses

Manganese doped lithium strontium borate glasses with chemical composition 25Li2O-15SrO-(60-x)B2O3-xMnO are prepared through the classical melt-quenching method and characterized by various techniques like XRD, DSC, optical absorption, EPR, Impedance spectra and AC conductivity. The XRD and DSC studies revealed the amorphous glassy nature of the prepared samples. The optical absorption spectra of the prepared inorganic glassy samples depict a single extensive absorption band at 470 nm attributed to the 6A1g(S)→4T1g(G) transition of Mn2+ ions belonging to d5 configuration in the octahedral symmetry sites. These spectra also substantiated that the octahedral Mn2+ ions were prevailing up to 0.8 mol% of MnO. The optical band gap energy and Urbach energies were evaluated from these spectra. The EPR spectra show three resonance signals positioned at g ≈ 2.0, 3.1 and 4.3 due to the Mn2+ paramagnetic ions. The resonance peak perceived at g ≈ 2.0 gives a predominant six-line hyperfine structure (hfs), a principal signature of Mn2+ ions. The hyperfine constant (Aavg), spin concentration (N), paramagnetic susceptibility (χ) and zero-field splitting (D) parameters of the prepared glass samples were evaluated and analyzed. The Nyquist (Cole-Cole) plots exhibit only one well-shaped semicircle (single-phase) throughout all the temperatures, which confirms the good homogeneity of the current glass system. The AC conductivity values of the prepared glassy samples are amplified with temperature and frequency. The AC conductivity values changed from 10−8 to 10−3 Ω−1cm−1. The LSBM8 glass sample has the highest AC conductivity; hence these glassy inorganic materials are suitable for solid-state battery applications and other opto-electronic device applications.

Hyperfine structure and absolute frequency of 127I2 transitions at 514 nm for wavelength standards at 1542 nm

The hyperfine structures of the P(57)45-0, P(91)48-0, and R(73)46-0 lines of molecular iodine ( 127 I 2 ) at 514 nm were studied using third-harmonic generation of a 1542 nm external-cavity diode laser and Doppler-free spectroscopy. The frequencies of the 1542 nm diode laser locked to the hyperfine transitions of these iodine lines are close to those of the P(16) transition in the ν 1 + ν 3 band of acetylene ( 13 C 2 H 2 ), which is used as a wavelength standard for telecom applications. The absolute frequencies of the observed 59 iodine hyperfine transitions were determined with an uncertainty of 5.4 kHz (fractional uncertainty of 9.3 × 10 − 12 ). Highly accurate hyperfine constants were obtained through fitting of the measured hyperfine splittings to a four-term Hamiltonian that includes electric quadrupole, spin–rotation, tensor spin–spin, and scalar spin–spin interactions with an uncertainty of a few kHz. The observed hyperfine transitions provide wavelength standards for telecom applications with various optical frequencies and reduced uncertainties compared with the acetylene wavelength standard.