Hyperfine Interaction Constants Research Articles

HFS92: A program for relativistic atomic hyperfine structure calculations

We describe a program for the computation of magnetic dipole and electric quadrupole diagonal ( A J , B J ) and off-diagonal ( A J, J−1 , B J, J−1 , B J, J−2 ) hyperfine interaction constants. Approximate atomic wavefunctions are assumed to be linear combinations of configuration state functions, which are, in turn, constructed from four-component spin-orbitals to be many-particle eigenfunctions of the parity and angular momentum operators.

Large-scale multiconfiguration Hartree-Fock and configuration-interaction calculations of the transition probability and hyperfine structures in the sodium resonance transition

Results from large-scale multiconfiguration Hartree-Fock (MCHF) and configuration-interaction (CI) calculations of the transition probability and hyperfine structures in the sodium 3s${\mathrm{}}^{2}$S-3p${\mathrm{}}^{2}$P resonance transition are presented. In the calculations the orbital sets of the initial and final state wave functions were not restricted to be the same, but were optimized independently. The evaluation of the transition matrix elements was done using a technique where the two orbital sets are transformed so as to become biorthonormal, in which case standard Racah algebra can be used. Three-particle effects were taken into account in the CI calculations and were found to be important for the hyperfine structures, but less important for the transition probability. The calculated transition probability is in perfect agreement with the most recent experimental values, thus resolving the long-standing disagreement between theory and experiment. Also the 3s${\mathrm{}}^{2}$${\mathit{S}}_{1/2}$ and 3p${\mathrm{}}^{2}$${\mathit{P}}_{1/2,3/2}$ hyperfine interaction constants are in very good agreement with available experimental values. \textcopyright{} 1996 The American Physical Society.

Microwave spectrum of the FS2 radical in the ground electronic X̃ 2A″ state

The FS2 radical has been detected in the glow discharge of the SF6 gas by microwave spectroscopy. Both a-type and b-type rotational transitions with the fine and hyperfine structure were observed in the millimeter-wave range of 120–185 GHz. The least-squares analysis for the 440 line frequencies led to the determination of the rotational constants, the centrifugal distortion constants, the spin-rotation interaction constants with the centrifugal distortion corrections, and the hyperfine interaction constants. Especially, the off-diagonal constants (εab+εba)/2 and Tab were determined in good precision because some nearly degenerate energy levels were mixed strongly by the off-diagonal spin-rotation interaction, which separated the energy levels up to 3 GHz and even induced the forbidden transitions to be observed strongly. The spin density on the fluorine atom and the chemical bond moments were derived for FS2, and the possible signs of Tab and (εab+εba)/2 were discussed. The behaviors of the FS2 radical and other related transient species in the SF6-discharge system were compared by using the corresponding rotational transitions observed in the microwave spectra.

Electron-nuclear double resonance of deep-boron acceptors in silicon carbide

Electron-nuclear double resonance spectra of deep-boron acceptors in silicon carbide have been observed. The quadrupole and hyperfine interaction constants are determined. A sharp decrease of the quadrupole interaction and suppression of the anisotropic part of the hyperfine interaction, as compared with shallow-boron acceptors, are found. The observed effects are explained by the motion of holes inside the deep-boron acceptor.

Evidence for existence of hydrogen-related dangling bonds in hydrogenated amorphous silicon

We have observed an electron-nuclear double resonance signal due to the 2D nucleus in sputtered deuterated amorphous Si (a-Si: D). The frequency of the signal is consistent with that estimated from the hyperfine interaction constant of a dangling bond with a 1H nucleus in hydrogenated amorphous Si (a-Si: H). This result provides further evidence for the existence of H-related (D-related) dangling bonds, that is dangling bonds having H(D) at a nearby site, in a-Si: H (a-Si: D) containing a large amount of H (D).

Molecular structure of the linear C3H radical: Microwave spectrum of the 13C substituted species

The rotational spectra of three 13C isotopic species of the linear C3H radical in the 2Πr ground vibronic state and the 2Σμ vibronic state of the ν4 (HCC bending) vibrational mode were observed by using a source-modulated spectrometer. The radical was produced in a free-space cell by a glow discharge in a mixture of C2H2, He, and 13CO. The rotational, spin-rotation interaction, Λ-type doubling, and hyperfine interaction constants were determined from the analysis of the observed spectra, where vibronic interaction between the 2Πr and 2Σμ states was taken into account. The rs structure of C3H, denoted by CαCβCγH, was derived from the rotational constants for the normal, deuterated, and three 13C species: rs(Cα–Cβ)=1.3263(1) Å, rs(Cβ–Cγ)=1.2539(2) Å, and rs(Cγ–H)=1.0171(1) Å. The short C–H distance is interpreted in terms of a large amplitude motion of the ν4 mode, whose vibrational energy is very low due to the Renner–Teller effect. An ab initio molecular orbital calculation was carried out, and the structure in which the HCC angle is bent was found to be slightly more stable than the linear structure. The spin densities of three carbon atoms are derived from the hyperfine interaction constants, and they are discussed in connection to the quasilinear nature of the molecule.

Sub-Doppler spectroscopy of 89Y

Sub-Doppler resolution of atomic transitions is obtained by spatially resolved laser induced fluorescence in a diverging atomic beam created by laser ablation. Resonances are spatially separated by relativistic effects experienced between the probing radiation and the moving particles thus proving that it is a high-quality atomic beam. Fast neutral atomic beams of 89Y having centroid energies up to 12 eV are interrogated with tuned, single-frequency laser light. Narrow, spatially separated points of light move along the probe axis and are imaged by detecting only the zero-velocity components of the fluorescence. Accordingly, the Y 2D3/2→Y 2D03/2 transition centered near 16 146 cm−1 is resolved into its hyperfine components with line widths on the order of 55 MHz and with an equivalent resolution of ±5 MHz (±0.0002 cm−1). The upper level hyperfine interaction constant derived from level splitting is +89±5 MHz. An equivalent collimation ratio of 9 mrad is estimated for the expanding pulsed atomic beam. We propose that laser ablation of selected targets provides a unique source of neutral or ionic ground-state atoms and molecules for spectroscopic studies. Details of these experiments are discussed and analyzed.

Electron paramagnetic resonance of Eu2+ in the dilute magnetic semiconductor Pb1-xEuxSe (x=0.013) with a cubic structure

Detailed X-band (about 9.5 GHz) electron paramagnetic resonance (EPR) measurements were carried out at 295, 77 and 4.2 K on the Eu2+ ion in a Pb1-xEuxSe single crystal. The values of the spin-Hamiltonian parameters have been determined by a simultaneous fitting of all the EPR line positions recorded for various orientations of the external magnetic field in the [010] plane using a rigorous least-squares fitting procedure. The absolute sign of the zero-field splitting parameter b4 was determined to be positive from the relative intensities of lines at liquid-helium temperature (4.2 K). The excellent fit of the line positions to a cubic spin Hamiltonian confirms that the site symmetry for Eu2+ ions is, indeed, cubic in the Pb1-x,Eux,Se single crystal over the temperature range 4.2-295 K. The Dynosian shape of the EPR lines indicates the metallic nature of the Pb1-xEuxSe sample. The nearest-neighbour Eu2+-Eu2+ exchange interaction has been estimated to be 20.4 GHz (antiferromagnetic) from the exchange pair EPR spectrum at 4.2 K. The hyperfine interaction constants for the isotopes 151Eu and 153Eu have been estimated.

Doppler free ?dark resonances? for hyperfine measurements and isotope shifts in Ca+ isotopes in a Paul trap

We have observed “dark resonances” in theA-type level structure, formed by the 4S1/2 ground state, the 4P1/2 excited state and the low lying metastable 3D3/2 state in the Calcium ion, confined in a Paul radio-frequency trap. These Doppler-free and potentially very narrow resonances were used to determine the magnetic dipole hyperfine interaction constant A for the 4P1/2 and 3D3/2 state of43Ca+, giving −142(8) MHz and −48.3(1.6) MHz, respectively. From measurements of the P-D (E1) and S-D (E2) transition wavelength in a mixture of43Ca+ and40Ca+ we determined the isotope shifts of these lines.

Multiconfiguration Hartree-Fock calculations of low-lying excited 2S states in lithium.

The hyperfine interaction constants, specific-mass-shift parameters, and total energies for the 3s${\mathrm{}}^{2}$S and 4s${\mathrm{}}^{2}$S states in lithium were calculated using the multiconfiguration Hartree-Fock method. The configuration expansions were obtained with the active space method, where configuration state functions are generated by excitations from the reference configuration to an active set of orbitals. The active set was increased in a systematic way, allowing the convergence of the studied parameters to be monitored. The obtained nonrelativistic energies are close to the lowest-upper-bound estimates from Hylleraas calculations. Whereas the convergence rate of the hyperfine interaction constants with respect to the increasing basis in the Hylleraas calculations degrades appreciably for higher states in the Rydberg series, no such effect could be seen for the multiconfiguration Hartree-Fock calculations. The uncertainties of the calculated hyperfine interaction constants are estimated to be less than three parts in a thousand for both of the studied states. The value for the 3s${\mathrm{}}^{2}$S state is in excellent agreement with results from relativistic many-body perturbation theory calculations, but is well outside the error bars from a recent precision measurement using Stark spectroscopy.

The influence of 13C nuclei on quantum beats in the recombination luminescence of radical ion pairs undergoing ion-molecular charge transfer

Abstract The presence of 13 C nuclei with high constants of hyperfine interaction (hfi) can change essentially the quantum beat frequency in some subensembles of recombining radical ion pairs. The corresponding disturbance of the total beat coherence due to the presence of 13 C nuclei is increased by ion-molecular charge transfer processes. The theoretical investigation of a model system, described in the present paper, shows that under some conditions the ion-molecular charge transfer can even lead to an increasing beat decay decrement with increasing concentration of the reactant involved in the charge transfer. This is the case when due to the presence of 13 C nuclei with high hfi constants in one of the radical ions its hyperfine structure (hfs) is splitted into widely spaced spectral groups. Averaging of this two-range hfs during ion-molecular charge transfer can be the reason for the unusual concentration dependence of the decay decrement of recombination luminescence beats of radical ion pairs.

Microwave Spectrum of the Linear C5D Radical

The rotational spectral lines of the linear C5D radical in the 2Π electric ground state are observed with a source-modulation microwave spectrometer and a Fourier-transform microwave spectrometer. Forty-eight spectral lines in the 173-279 GHz region and 10 in the 11-16 GHz region are measured and 10 molecular constants, including hyperfine interaction constants, are determined by a least-squares method. Frequencies of low-J rotational transitions of C5D are calculated for radio astronomical observations.

MCHF+BP Approaches of Hyperfine Interaction Constants in 45ScII11The project supported by the Foundation of 863 High Technology Project and Partially by the Foundation of Chinese Academy of Engineering Physics.

Multi-configuration Hartree–Fock and configuration interaction calculations of hyperfine structure constants for 3d2 3P states of ScII are reported. It is very important to consider core polarization (especially spin polarization) and core-core correlation as well as valence correlation for accurate calculation of hyperfine constants. The relativistic correction (through Breit–Pauli approximation) as well as finite-nuclear-mass and fnite-nuclear-size-corrected values of the hyperfine constants for ScII are in good agreement with the most accurate experimental values and better than other ab initio theoretical results.

Large-scale multiconfiguration Dirac-Fock calculations of hyperfine interaction constants for nd2 levels of Sc+ and Y+

The multiconfiguration Dirac-Fock model is employed to study the effects of relativity and electron correlation on the hyperfine interaction constants of the 3${\mathit{d}}^{2}$ $^{3}$${\mathit{P}}_{1}$, $^{3}$${\mathit{P}}_{2}$, $^{1}$${\mathit{D}}_{2}$, and $^{3}$${\mathit{F}}_{2}$ levels of ${\mathrm{Sc}}^{+}$ and the 4${\mathit{d}}^{2}$ $^{3}$${\mathit{P}}_{1}$ level of ${\mathrm{Y}}^{+}$. The wave function expansions are obtained with the active space method, where configuration state functions of a specific parity and J value are generated by excitations from the most important reference configurations to an active set of orbitals. The active set is then increased in a systematic way, allowing the convergence of the hyperfine interaction constants to be studied. It is demonstrated that expansions generated by single excitations from the reference configurations, together with the most important double excitations, account for the dominant contributions to the hyperfine interaction constants and lead to very good agremeent between theoretical and experimental values. To obtain converged values of these constants within the single excitation approach, typically a few thousand configuration state functions are needed.

Mn 2+ EPR investigation of sol-gel process in silica xerogels at 77 K

The EPR spectrum of the Mn 2+ ion has been used as a diagnostic tool at liquid-nitrogen temperature (77 K) to investigate the structural evolution of SiO 2 xerogels as a function of temperature during their calcination, as well as during subsequent aging. The positions of the Mn 2+ hyperfine lines were used to estimate the g-factor, the hyperfine interaction constant ( A) and the zero-field splitting parameter ( D) for the Mn 2+ ion in the various xerogels. The values of the parameters g, A of the xerogels were found to be, within experimental error, independent of the firing temperature as well as that of aging. However, the splitting of the forbidden hyperfine lines, and thus the value of D, was found to be significantly different in the samples prepared at firing temperatures of 360°C and below from those prepared at firing temperatures of 440°C and above; they remained independent of aging.

Further evidence for the B −SI-C + model of the boron acceptor in 6H silicon carbide from a theoretical analysis of the hyperfine interactions

A semiempirical analysis of the sizes and signs of the small boron hyperfine interaction constants as determined previously by electron nuclear double resonance in boron-doped 6H silicon carbide shows that the B−SI-C+ model of this centre can account for the highly unusual feature of small isotropic and anisotropic boron hyperfine constants that are positive and negative, respectively.

Precision measurement of the hyperfine structure and nuclear moments of 180mTa by laser-rf double resonance.

Hyperfine structure of the 5${\mathit{d}}^{3}$6${\mathit{s}}^{2}$ $^{4}$${\mathit{F}}_{3/2}$ ground state in $^{180\mathit{m}}\mathrm{Ta}$ i was precisely measured by means of atomic-beam laser-rf double-resonance spectroscopy. Hyperfine-interaction constants A and B for the ground state $^{4}$${\mathit{F}}_{3/2}$ were determined with accuracies of 3 and 10 ppm, respectively. The nuclear electric quadrupole moment was derived, as well as a precise value of the magnetic moment for $^{180\mathit{m}}\mathrm{Ta}$ (${\mathit{I}}^{\mathrm{\ensuremath{\pi}}}$=${9}^{\mathrm{\ensuremath{-}}}$): the magnetic dipole moment is ${\mathrm{\ensuremath{\mu}}}_{\mathit{I}}^{180\mathit{m}}$=+4.825(11)${\mathrm{\ensuremath{\mu}}}_{\mathit{N}}$ and the spectroscopic quadrupole moment is ${\mathit{Q}}_{\mathit{s}}^{180\mathit{m}}$=+4.946(20)b.

The microwave spectrum of the ClS2 free radical

The rotational spectrum of the ClS2 free radical in the gaseous phase has been observed in the millimetre- and submillimetre-wave regions. The ClS2 radical was generated by a dc glow discharge in either S2Cl2 or SCl2. Both a- and b-type R-branch transitions, most of which were split into two fine structure components, were detected for both of the 35Cl and 37Cl isotopic species in the ground vibronic state. As expected from the small hyperfine interaction constants reported by an electron spin resonance (ESR) study, the hyperfine structure was resolved for none of the transitions observed in the present study. Analysis of the observed transition frequencies yielded rotational and centrifugal distortion constants and also spin–rotation interaction constants with their centrifugal corrections. The spin–rotation interaction constants obtained in the present study were consistent with g values of the ESR study. The rotational constants of the two isotopic species led to the structure parameters r(S—S) = 1.906 (7) Å, r(S—Cl) = 2.071 (5) Å, and θ(SSCl) = 110.3 (4)°. A harmonic force field was derived from the observed centrifugal distortion constants and inertial defects combined with the ν1 frequency reported in literature on electronic spectroscopy. This harmonic force field yielded the ν2 and ν3 frequencies (445 (21) and 213.0 (2) cm−1, respectively, for 35ClS2), which differed considerably from the values reported previously.

Microwave spectrum and molecular structure of the HS2 radical

Rotational spectral lines of the HS2 and DS2 radicals in the 2A″ ground electronic state are detected by a source-modulation microwave spectrometer combined with a free-space cell. The HS2 radical is produced in the cell by discharging a pure H2S gas. The spectrum of DS2 is observed by using a mixture of H2S and D2. The rotational constants, the centrifugal distortion constants, the spin-rotation interaction constants with their centrifugal distortion corrections, and the hyperfine interaction constants for the hydrogen nucleus are determined by least-squares analyses. The harmonic force constants are evaluated from the observed centrifugal distortion constants in combination with the vibrational frequencies reported previously. The zero-point average structure of HS2 is determined from the observed rotational constants of HS2 and DS2 with the aid of the harmonic force constants: rz(S—S) = 1.9650 (7) Å, rz (S—H) = 1.362 (3) Å, and αz (HSS) = 101/7 (4)° (1 Å = 10−10 m). The equilibrium distances for the S—S and S—H bonds are derived to be 1.9606 (7) Å and 1.352 (3) Å, respectively, by assuming the anharmonic constants of the corresponding diatomic molecules.

Core-polarization on hyperfine interaction constants in the metastable 3d 2 state of 45ScII

Multi-configuration Hartree-Fock and configuration interaction calculations of hyperfine structure constants for 3d 2 states of ScII are reported. It is very important to consider core-polarization (especially spin-polarization) and core-core correlation as well as the valence correlation in accurate calculations of hyperfine constants. The relativistic corrections (through the Breit-Pauli approximation) as well as finite-nuclear-mass and finite-nuclear-size corrected values of the hyperfine constants for ScII are in good agreement with the most accurate experimental values within 5%.