Magnetic Hyperfine Coupling Constants Research Articles

Towards in-jet resonance ionization spectroscopy: An injection-locked Titanium:Sapphire laser system for the PALIS-facility

This article presents a pulsed narrowband injection-locked Titanium:Sapphire laser aimed for high-resolution in-jet resonance ionization spectroscopy at the SLOWRI/PALIS at RIKEN. The laser has been integrated into the PALIS laser laboratory enabling it to be utilized with the existing broadband Titanium:Sapphire and dye lasers. The seed efficiency has been evaluated to be close to unity over the master laser wavelength range ∼ 753 to 791 nm, and the slope efficiency, namely the ratio of the pump power to the output power, was determined to be ∼ 30 % at 780 nm. A two-step ionization scheme with 386.4016 nm first step and 286.731 nm second step into an autoionizing state was developed for resonance ionization spectroscopy of 93Nb. Magnetic hyperfine coupling constants of 1866±8 MHz and 1536±7 MHz were measured for the ground and excited state, respectively, in a good agreement with the literature values. A Gaussian dominated Voigt linewidth of 434.5 ± 7.4 MHz was extracted from the hyperfine spectra measured for niobium. In addition, the resolution of the in-jet resonance ionization in PALIS is estimated through numerical methods.

Determination of hyperfine structure constants of 5D5/2 and 7S1/2 states of rubidium in cascade atomic system

We present a method to precisely determine the hyperfine structure constants of the rubidium 5D5/2 and 7S1/2 states in a cascade atomic system. The probe laser is coupled to the 5S1/2→5P3/2 hyperfine transition, while the coupling laser is scanned over the 5P3/2→5D5/2(7S1/2) transition. The high-resolution double-resonance optical pumping spectra are obtained with two counter-propagating laser beams acting on rubidium vapor. The hyperfine splitting structures are accurately measured by an optical frequency ruler based on the acousto-optic modulator, thus, the magnetic dipole hyperfine coupling constant A and quadrupole coupling constant B are determined. It is of great significance for the atomic hyperfine structure and fundamental physics research.

Characterization of the [18.28]0--a3Δ1 (0,0) band of tantalum nitride, TaN.

The [18.28]0--a3Δ1 (0,0) band near 647 nm of tantalum nitride, TaN, has been recorded and analyzed field-free and in the presence of static electric and magnetic fields. The fine and hyperfine parameters for the a3Δ1 and [18.28]0- states are determined. The 181Ta(I = 7/2) axial nuclear electric quadrupole coupling constant, eQq0, and the effective magnetic hyperfine coupling constant, h1, are used to garner insight into the nature of electronic states. The Stark tuning of the P(2) and Q(1) lines was analyzed to determine the molecular frame permanent electric dipole moment, μ→el, for the a3Δ1 state of 4.49 ± 0.09 D. The Zeeman effect on the P(1) line was analyzed to determine an upper limit of the magnetic moment, μ→m, for the a3Δ1 state. Scalar-relativistic coupled-cluster calculations for eQq0 and μ→el of the a3Δ1 state are also reported and compared with experimental results. The determined properties are compared with the predicted values and the implication of the proposed scheme for determination of the 181Ta magnetic quadrupole moment is discussed.

Communication: Viewing the ground and excited electronic structures of platinum and its ion through the window of relativistic coupled cluster method.

Highly accurate electronic structure calculations are often needed to supplement scant experimental data. We report the ground 3D3 and some selected low lying excited/ionized states of Pt and its ions obtained using the Fock space multireference coupled cluster method with four-component relativistic spinors. The present work establishes the stability of the 2S1/2 state of its negative ion and reproduces the binding energy of this state within 10 cm-1. The first ionization potential (cm-1) is estimated to be 72 005, deviating from the experiment by just 200 (0.3%). We also report the magnetic hyperfine coupling constants (A) of Pt and its ions. The present calculation provides the A value (GHz) of the 3D3 state of Pt to be 5.78 exhibiting very good agreement with the experimental data of 5.70. To our knowledge, this is the first relativistic ab initio calculation of the ionization potential and magnetic hyperfine coupling constant for the neutral and ionic states of Pt at a high level of correlation treatment.

Determination of the hyperfine coupling constants of the 5D5/2 state of 85Rb atoms by using high signal-to-noise ratio electromagnetically-induced transparency spectra

We report the hyperfine splitting measurement of the 85Rb 5D5/2 state by electromagnetically induced transparency spectroscopy with high signal-to-noise ratio in the 85Rb 5S1/2-5P3/2-5D5/2 ladder-type system (m 780 nm + 776 nm). The frequency calibration is performed by employing a phase-type electro-optic modulator with a confocal Fabry-Perot cavity. From the measured hyperfine splittings among the manifolds of (F=5), (F=4) and (F=3) of the 85Rb 5D5/2 state, we determine the magnetic dipole hyperfine coupling constant (A= (-2.222 0.019) MHz) and the quadrupole coupling constant (B= (2.664 0.130) MHz) of 5D5/2 state of 85Rb atoms.

Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70–102 GHz region

Chirped-pulse millimeter-wave (CPmmW) spectroscopy is the first broadband (multi-GHz in each shot) Fourier-transform technique for high-resolution survey spectroscopy in the millimeter-wave region. The design is based on chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy [G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, and B. H. Pate, Rev. Sci. Instrum. 79, 053103 (2008)], which is described for frequencies up to 20 GHz. We have built an instrument that covers the 70-102 GHz frequency region and can acquire up to 12 GHz of spectrum in a single shot. Challenges to using chirped-pulse Fourier-transform spectroscopy in the millimeter-wave region include lower achievable sample polarization, shorter Doppler dephasing times, and problems with signal phase stability. However, these challenges have been partially overcome and preliminary tests indicate a significant advantage over existing millimeter-wave spectrometers in the time required to record survey spectra. Further improvement to the sensitivity is expected as more powerful broadband millimeter-wave amplifiers become affordable. The ability to acquire broadband Fourier-transform millimeter-wave spectra enables rapid measurement of survey spectra at sufficiently high resolution to measure diagnostically important electronic properties such as electric and magnetic dipole moments and hyperfine coupling constants. It should also yield accurate relative line strengths across a broadband region. Several example spectra are presented to demonstrate initial applications of the spectrometer.

Measurement of hyperfine structure within the6P3/2excited state ofI115n

Using a two-step, two-color laser spectroscopy technique, we have completed a measurement of the hyperfine structure within the $(5{s}^{2}6p)$ ${^{2}P}_{3/2}$ excited state in $^{115}\text{I}\text{n}$ $(I=9/2)$. A frequency stabilized GaN diode laser at 410 nm is locked to the $5{P}_{1/2}\ensuremath{\rightarrow}6{S}_{1/2}$ ground-state transition and a second 1291 nm diode laser is scanned over the $6{S}_{1/2}\ensuremath{\rightarrow}6{P}_{3/2}$ transition to produce hyperfine spectra for the $6{P}_{3/2}(F=3,4,5,6)$ manifold. We find the hyperfine splittings of consecutive sublevels to be as follows: $\ensuremath{\Delta}{\ensuremath{\nu}}_{4\ensuremath{-}3}=275.25(42)\text{ }\text{MHz}$, $\ensuremath{\Delta}{\ensuremath{\nu}}_{5\ensuremath{-}4}=384.05(71)\text{ }\text{MHz}$, and $\ensuremath{\Delta}{\ensuremath{\nu}}_{6\ensuremath{-}5}=517.48(44)\text{ }\text{MHz}$. The magnetic dipole, electric quadrupole, and magnetic octupole hyperfine coupling constants derived from these three splittings are, respectively, $a=79.33(7)\text{ }\text{MHz}$, $b=62.5(5)\text{ }\text{MHz}$, and $c=\ensuremath{-}0.04(4)\text{ }\text{MHz}$. The measured value of the dipole constant, $a$, agrees to within 2% with a recent theoretical prediction.

First principles study of local electronic and magnetic properties in pure and electron-dopedNd2CuO4

The local electronic structure ofNd2CuO4 is determined from ab initio cluster calculations in the framework of density functional theory.Spin-polarized calculations with different multiplicities enable a detailed study of the chargeand spin density distributions, using clusters that comprise up to 13 copper atoms in theCuO2 plane. Electron doping is simulated by two different approaches and the resulting changes in the localcharge distribution are studied in detail and compared to the corresponding changes in hole-dopedLa2CuO4. The electric field gradient (EFG) at the copper nucleus is investigated and goodagreement is found with experimental values. In particular a careful study ofthe various contributions to the EFG exhibits that the drastic reduction of themain component of the EFG in the electron-doped material with respect toLa2CuO4 is due to a reduction of the occupancy of the3d3z2−r2 atomic orbital. Furthermore, the chemical shieldings at the copper nucleus are determinedand are compared to results obtained from nuclear magnetic resonance (NMR)measurements. The magnetic hyperfine coupling constants are derived from the spindensity distribution calculated for different spin multiplicities.

Nuclear ordering and excitations in [formula omitted

The energy splitting of Nd nuclear levels and Nd nuclear polarization in NdFeO 3 have been studied by using high resolution inelastic neutron backscattering with simultaneous neutron diffraction at temperatures between 100 mK and 15 K. Inelastic peaks are observed below 4.5 K with a corresponding energy splitting Δ E = 1.24 μ eV below 0.9 K. The Nd nuclear magnetic moments are polarized below 1 K with a maximal polarization of 17% observed at 100 mK. Both these phenomena directly observed in NdFeO 3 are described by assuming a magnetic hyperfine coupling model. It is found that the present experimental data on NdFeO 3 and the literature data concerning Nd 2 CuO 4 can be consistently described by using the same value of the magnetic hyperfine coupling constant A = 1.10 ( 5 ) μ eV / μ B .

A theoretical study of the fine and hyperfine interactions in the NCO and CNO radicals.

The geometries, the harmonic vibrational frequencies, and the Renner-Teller parameter have been reported for the NCO(+)(X (3)Sigma(-)), NCO(X (2)Pi,A (2)Sigma(+),B (2)Pi,2 (2)Sigma(+)), NCO(-)(X (1)Sigma(+)), CNO(+)(X), CNO(X (2)Pi,A (2)Sigma(+),B (2)Pi,2 (2)Sigma(+)), and CNO(-)(X (1)Sigma(+)) systems at the full valence-complete active space self-consistent-field (fv-CASSCF) level of theory. The (2)Pi electronic states of the NCO and CNO radicals have two distinct real vibrational frequencies for the bending modes and these states are subject to the type A Renner-Teller effect. The total energy of CNO(+) without zero point energy correction of the linear geometry is approximately 31 cm(-1) higher than the bent geometry at the fv-CASSCF level and the inversion barrier vanishes after the zero point energy correction; therefore, the ground state of the CNO(+) may possess a quasilinear geometry. The spin-orbit coupling constants estimated using atomic mean field Hamiltonian at the fv-CASSCF level of theory are in better agreement with the experimental values. The excitation energies, the electron affinity, and the ionization potential have been computed at the complete active space second order perturbation theory (CASPT2) and the multireference singles and doubles configuration (MRSD-CI) levels of theory. The computed values of the electric hyperfine coupling constants for the (14)N atom in the ground state of the NCO radical agree well with the experimental data. The magnetic hyperfine coupling constants (HFCC's) have been estimated employing the configuration selected MRSD-CI and the multireference singles configuration interaction (MRS-CI) methods using iterative natural orbitals (ino) as one particle basis. Sufficiently accurate value of the isotropic contribution to the HFCC's can be obtained using an MRS-CI-ino procedure.

Theoretical study of fine and hyperfine interactions in N3+, N3⋅, and N3−

The geometries and the harmonic vibrational frequencies have been computed for the N3+(X̃ 3Σg−,ã 1Δg,b̃ 1Σg+,Ã 3Πu,1 1Πu), N3⋅(X̃ 2Πg,Ã 2Σu+,1 2Σg+), and N3−(X̃ 1Σg+) systems using the full-valence complete active space self-consistent-field (CASSCF) vectors. The systems N3+(Ã 3Πu,1 1Πu) and N3⋅(X̃ 2Πg) possess two distinct real frequencies for the bending modes. The energy for both components increases upon bending and these states are subject to the type A Renner–Teller effect. The energetics and the dynamical properties have been studied at the complete active space second order perturbation theory (CASPT2) and the multireference singles and doubles configuration interaction (MRSD–CI) levels of theory. The spin–orbit coupling constants, ASO in N3+(Ã 3Πu) and N3⋅(X̃ 2Πg) are obtained by employing the atomic mean field spin–orbit Hamiltonian and these are about 3 cm−1 from the experiment. The nuclear quadrupole coupling constants at various nitrogen centers have been predicted in all the systems by employing the CASSCF, the CASPT2 and the MRSD–CI-ino (iterative natural orbital procedure) methods. The magnetic hyperfine coupling constants (hfcc’s) have been computed for the various N14’s in N3+(X̃ 3Σg−,Ã 3Πu) and N3⋅(X̃ 2Πg,Ã 2Σu+,1 2Σg+) at the configuration selected MRSD–CI-ino level of theory using weighted threshold criteria for the configuration selection.

Saturated absorption spectroscopy of Xe using a GaAs semiconductor laser

Doppler-free absorption spectrum from 5P 56S to 5P 56P transitions of Xe in a hollow cathode discharge was measured in the wavelength region from 810 to 910 nm. The saturated dip signals detected by a frequency modulated probe beam were doubly AM-modulated by a pump beam chopped using a conventional mechanical chopper. The Doppler background was greatly reduced by detection using a second lock in amplifier synchronous to the chopping signal. The isotope shifts of even mass 136−128Xe in natural abundance were resolved for the five transitions from the metastable states of J=2 and 0, while in the transitions from the J=1 states were partially resolved. The nuclear magnetic and quadrupole hyperfine coupling constants of 131Xe and 129Xe determined are listed with those reported previously. The specific mass shifts and the field shifts were estimated using the relation given by King's diagram and compared with those obtained from the changes in the mean square-radii of the nuclear charge distribution.

Evidence for Antisymmetric Exchange in Cuboidal [3Fe−4S]+Clusters

Iron−sulfur clusters with [3Fe−4S] cores are widely distributed in biological systems. In the oxidized state, designated [3Fe−4S]+, these electron-transfer agents have an electronic ground state with S = 1/2, and they exhibit EPR signals centered at g = 2.01. It has been established by Mössbauer spectroscopy that the three iron sites of the cluster are high-spin Fe3+, and the general properties of the S = 1/2 ground state have been described with the exchange Hamiltonian Hexch = J12S1·S2 + J23S2·S3 + J13S1·S3. Some [3Fe−4S]+ clusters (type 1) have their g-values confined to the range between g = 2.03 and 2.00 while others (type 2) exhibit a continuous distribution of g-values down to g ≈ 1.85. Despite considerable efforts in various laboratories no model has emerged that explains the g-values of type 2 clusters. The 4.2 K spectra of all [3Fe−4S]+ clusters have broad features which have been simulated in the past by using 57Fe magnetic hyperfine tensors with anisotropies that are unusually large for high-spin ferric sites. It is proposed here that antisymmetric exchange, HAS = d·(S1 × S2 + S2 × S3 + S3 × S1), is the cause of the g-value shifts in type 2 clusters. We have been able to fit the EPR and Mössbauer spectra of the 3Fe clusters of beef heart aconitase and Desulfovibrio gigas ferredoxin II by using antisymmetric exchange in combination with distributed exchange coupling constants J12, J13, and J23 (J-strain). While antisymmetric exchange is negligible for aconitase (which has a type 1 cluster), fits of the ferredoxin II spectra require |d| ≈ 0.4 cm-1. Our studies show that the data of both proteins can be fit using the same isotropic 57Fe magnetic hyperfine coupling constant for the three cluster sites, namely a = −18.0 MHz for aconitase and a = −18.5 MHz for the D. gigas ferredoxin. The effects of antisymmetric exchange and J-strain on the Mössbauer and EPR spectra are discussed.

Density functional study of electronic, magnetic and hyperfine properties of [M(CN) 5NO] 2− (M=Fe, Ru) and reduction products

The discrete variational method (DVM) in density functional theory (DFT) was employed to investigate the electronic structure of the complexes: [Fe(CN) 5NO] 2− (nitroprusside), [Fe(CN) 5NO] 3−, [Fe(CN) 4NO] 2−, [Ru(CN) 5NO] 2− and [Ru(CN) 5NO] 3−. Total energy calculations revealed that in pentacyanonitrosylferrate(I) and pentacyanonitrosylruthenate(I), which are paramagnetic ions containing one unpaired electron, the M–N–O bond angle is bent. From self-consistent spin-polarized calculations, the distribution of the unpaired electron in the paramagnetic complexes [Fe(CN) 5NO] 3−, [Fe(CN) 4NO] 2− and [Ru(CN) 5NO] 3− was obtained, as well as spin-density maps. A long-standing controversy regarding the configuration of [Fe(CN) 5NO] 3− was elucidated, and it was found that the unpaired electron in this complex is in an orbital primarily localized on π * (NO). Mössbauer quadrupole splittings on Fe and Ru were derived from calculations of the electric-field gradients. Magnetic hyperfine coupling constants on N of the NO ligand were also obtained for the paramagnetic complexes.

The microwave spectrum of the HSiS radical in the 2A′ ground electronic state

The rotational spectrum of the HSiS radical in its X 2A′ ground electronic state was detected by using a source-modulated microwave spectrometer combined with a glow discharge free space cell. The transient radical was generated by relatively weak d.c. discharge in a mixture of OCS and SiH 4. Observed spectral lines were a-type R-branch rotational transitions showing hyperfine structure due to the hydrogen nucleus. In total 133 spectral lines were measured for 38 rotational transitions of N = 13−12 to 18−17 in the frequency region of 215 to 301 GHz. Nineteen molecular constants including the magnetic hyperfine coupling constants of the hydrogen nucleus were precisely determined by a least-squares fit of the observed lines. The r 0 structure was derived from determined molecular constants: r 0( SiS) = 1.9537(19) A ̊ and ∠HSiS = 118.8(17)° on the assumption of r 0( SiH) = 1.5140 A ̊ , where the errors are due to the inertial defect. From the Fermi contact term observed the s character spin density for the hydrogen was determined to be 23.6%, indicating that the HSiS molecule is a σ radical like HCO( 2A′).

Phase transition sequence between fluid liquid-crystalline and interdigitated lamellar gel phases in mixed-chain diacyl phosphatidylcholine

The phase transition behavior of asymmetric phosphatidycholine with palmitic acid at the sn-1 position and capric acid at the sn-2 position (C16C10PC) has been examined by simultaneous differential scanning calorimetry and synchrotron X-ray diffraction complemented by electron spin resonance. The experiments were performed for a sequence of cooling, heating and recooling scans of aqueous dispersions of C16C10PC. The results showed that a single exothermic peak centered at 5°C appeared on the initial cooling. It coincided with a transition of a liquid-crystalline lamellar phase (d-spacing, 6.4 nm) directly into an interdigitated lamellar gel phase (d-spacing, 5.2 nm). An immediate reheating scan showed a single broad endothermic transition peak in the temperature range 3–10°C over which there was a direct transition from the interdigitated lamellar gel phase to the fluid liquid-crystalline lamellar phase with coexistence of the two phases in the region of the transition. Coexistence of phases was also inferred from ESR evidencing two different environments for 16 doxyl stearic acid probe. Unlike non-interdigitated gel phases of symmetric phospholipids, the interdigitated gel phase of C16C10PC is typified by a high value of the magnetic hyperfine coupling constant. This constant (16 Gauss) indicates around the nitroxide group a viscous highly ordered environment with hydrogen bonding within the interdigitated bilayer. The subsequent cooling scan was markedly different from the initial cooling scan since the thermogram showed two exothermic peaks. The first peak at 7°C, representing 30% of the overall enthalpy change, coincided with the conversion of fluid liquid-crystalline phase into non-interdigitated lamellar gel phase (d-spacing, 6.32 nm). The second peak at 5°C is observed when the interdigitated lamellar gel phase (d-spacing, 5.2 nm) takes place. This behavior is consistent with the buildup of extended lamellar sheets with low curvature induced by cooling down vesicles with high radius of curvature fusing when the interdigitated lamellar gel phase takes place beyond the transition temperature. Time-resolved DSC and X-ray diffraction show differences with ESR at the transition temperature which support the occurrence of a metastable non-interdigitated gel between the fluid and the interdigitated lamellar gel in the transition sequence.

An ab initio determination of the magnetic hyperfine structure of C 2 in the four lowest triplet states

The magnetic hyperfine coupling constants of C 2 are calculated for the four lowest triplet states ( 3Π u, 3Σ g −, 3Σ u +, 3Π g ) using various ab initio methods. The dependence of the hfcc's on the computational method is carefully studied to obtain an insight into the applicability of approximate methods in the calculation of magnetic hfcc's for larger C n clusters. Only MRD-CI/B K, QCISD(T), CCSD(T) and UMP4 are able to describe hfcc's accurately for all electronic states of C 2 while more approximate approaches (e.g. DFT, UMP2, UMP3, MRD-CI) fail in at least one state. The calculated values are compared with experimental data, and differences between the various electronic states are discussed by means of orbital relaxation effects and spin polarisation mechanisms.

Ab Initio Investigation of Vibrational Effects on Magnetic Hyperfine Coupling Constants in the X3Σg- State of B2H2

The influence of the vibrational motion on the magnetic hyperfine coupling constants (hfcc's) in the X3Σg- of B2H2 is investigated by means of ab initio methods. The present study clearly shows that for the isotropic hfcc's of the boron centers the incorporation of the vibrational effects is essential already for the vibrational ground state. For the boron center the isotropic hfcc's calculated for the lowest vibrational state (Aiso(11B) = −5.2 MHz) differ considerably from the value obtained at the equilibrium geometry (Aiso(11B) = −14.0 MHz) but agrees excellently with the experimental value (Aiso(11B) = −5.2 MHz) obtained previously. For the hydrogen centers and for all anisotropic hfcc's the effects are found to be much smaller. In the present study the averaged values for various vibrational states and isotopic effects are given.

ChemInform Abstract: Magnetic Hyperfine Coupling Constants in Free Radicals

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Hyperfine structure of the resonance lines of53Cr and lifetimes of some excited states of the Cr I spectrum

The hyperfine structure of the53Cr resonance linesa 7 S 3 ↔z 7 P 2,3,4 has been investigated by means of laser saturation spectroscopy. By comparison of the experimental signal curves with theoretically computed spectra the hitherto unknown sign of the magnetic hyperfine coupling constant in thea 7 S 3 ground state of53Cr could be determined unambigiously to be negative. Further the signs of the hfs coupling constants in thez 7 P states — so far only evaluated by theoretical reasoning — could be confirmed. Additionally the lifetimes of the statesz 7 P,z 5 P,f 7 D,z 5 F,e 7 D 5 andy 5 P 3 in the Cr I spectrum have been determined from the fluorescence decay after pulsed laser excitation.