Hyperfine Interaction Constants Research Articles

Microwave spectroscopy of the NBr radical in the X 3Σ− state

The microwave spectrum of the NBr radical in the X 3Σ− ground electronic state has been observed by a source modulated spectrometer. The NBr radical was generated in a free space cell by a dc glow discharge in a mixture of N2, Br2, and He. The spectrum with three spin components of both two isotopomers, N79Br and N81Br, was observed. The spectrum showed complicated splitting by the hyperfine interactions due to both bromine and nitrogen nuclei. The molecular constants including the magnetic hyperfine and nuclear quadrupolar hyperfine interaction constants were determined by analyzing the observed spectrum. The spin density of the unpaired electrons was estimated from the observed hyperfine coupling constants to be 73.4% and 22.4% on the nitrogen and the bromine atoms, respectively.

Microwave spectrum and molecular structure of the H2NS radical

The rotational spectral lines of the H2NS and D2NS radicals in the X̃2B1 electronic ground state are observed with a source-modulation microwave spectrometer and a Fourier-transform microwave spectrometer. Molecular constants including hyperfine interaction constants are determined for H2NS and D2NS by a least-squares method. By using the obtained centrifugal distortion constants and inertial defects, the harmonic force field is evaluated, and the frequency of the ν4 vibrational mode (out of plane) is calculated to be 325 cm−1. This value is much smaller than that of the related molecule H2CS, indicating a floppy motion along the out-of-plane mode. The zero-point vibrational average structure was determined as follows; rz(N–H)=1.000(5) Å, rz(N–S)=1.6398(13) Å, and ∠z(HNH)=118.9(7)°, where the numbers in parentheses represent three times the standard deviation.

Fourier transform millimeter-wave spectroscopy of the HCS radical in the A′2 ground electronic state

The 101–000 rotational transition of the HCS radical in the X̃ A′2 ground electronic state has been observed with a Fourier transform millimeter-wave spectrometer in combination with a pulsed discharge nozzle. The radical is produced by discharging a mixture of CH4 and H2S diluted in Ar. Six fine and hyperfine components are detected, and the effective rotational constant, spin–rotation interaction constant, and hyperfine interaction constants are determined accurately. The Fermi contact term of the hydrogen nucleus is found to be much smaller than that for the isovalent radical, HCO, indicating that the HCS radical is more close to a linear structure than the HCO radical.

Extraction of hyperfine anomalies without precise values of the nuclear magnetic dipole moment

A new method for extracting the hyperfine anomaly from experimental hyperfine structure constants is suggested. Instead of independent high-precision measurements of the nuclear magnetic dipole moment, precise measurements of magnetic dipole hyperfine interaction constants for two atomic states and a theoretical analysis can be used. This can lead to determination of hyperfine anomaly for radioactive isotopes where the nuclear magnetic dipole moment is not known with high accuracy.

The structure of dangling bonds having hydrogen at a nearby site in a-Si:H

We have deconvoluted the dangling bond ESR spectra into two components, one due to normal dangling bonds and the other to hydrogen-related dangling bonds in glow-discharge a-Si:H samples. The isotropic and anisotropic hyperfine interaction constants due to a hydrogen nucleus are estimated from the deconvolution. It is found that they are mutually related through a simple theoretical expression. The distance between the dangling bond site and hydrogen in the hydrogen-related dangling bond and relative densities of the above two types of dangling bonds are also estimated and discussed in correlation with the hydrogen content.

The manifestation of degenerate electron exchange in stimulated nuclear polarization at high magnetic fields

A detailed theoretical and experimental investigation of the degenerate electron exchange (DEE) effect on the stimulated nuclear polarization (SNP) intensity and spectra at high magnetic fields has been made. The theoretical description of DEE processes is performed in two different ways: (i) The numerical solution of equations of noncorrelated frequency migration theory and (ii) the analytical solution for simple two-site model for the dependence of the SNP intensity on the rate of DEE at low microwave (mw) field amplitudes ( B 1 ⪡ a, a is a constant of hyperfine interaction (HFI) of radical-ions) and low DEE rates ( aτ e ⪢ 1, τ e is the characteristic time of DEE). It is shown that the increase of DEE rate leads to the decrease of splitting in SNP spectra, and also to a substantial decrease of the SNP signal intensity due to an overlapping of hyper-fine structure lines with opposite signs. A numerical evaluation of DEE rate constants can be done by comparison of experimental and calculated spectrum shape in the case of fast DEE rates and from the dependence of SNP intensity in resonance on the concentration of diamagnetic molecules.

EPR studies of Er 3+, Nd 3+ and Ce 3+ in YAlO 3 single crystals

EPR spectra of Er 3+, Nd 3+ and Ce 3+ ions in YAlO 3 lattice have been studied. These spectra can be described by spin Hamiltonian with an effective spin S = 1 2 and rhombohedric symmetry. The g factors as well as the constants of hyperfine interaction of Nd 3+ and Er 3+ were obtained. It was stated that all the resonances which are upon the interest of this article, belong to the RE 3+ ions replacing the Y 3+ cations in the YAlO 3 lattice.

Microwave spectrum of HSiO in the X2A′ ground electronic state

The rotational spectrum of the HSiO radical has been measured in the millimeter- and submillimeter-wave regions. The radical is produced in a d.c. glow discharge plasma of a gaseous mixture of SiH 4 and N 2O. Molecular constants including magnetic hyperfine interaction constants of the hydrogen nucleus are determined accurately from the observed frequencies of 111 a-type R-branch transitions. A portion of quadratic force constants are derived from the centrifugal distortion constants and the inertial defect, and they are used to determine the zero point average structure of HSiO; r 1( SiO) = 1.5326(2) A ̊ and α 1(HSiO) = 116.8(1)°, where r 1(SiH) is assumed to be 1.5066 Å.

Fourier Transform Microwave Spectroscopy of13C-Substituted CCS Radicals

The rotational spectral lines of the13C isotopic species of CCS (13CCS, C13CS, and13C13CS) have been observed using a Fourier transform microwave spectrometer in combination with a pulsed-discharge nozzle. The hyperfine-resolvedJN= 10–01,JN= 21–10, andJN= 32–21transitions have been observed in the 11-, 22-, and 33-GHz regions, respectively, with an accuracy of about 5 kHz. The observed transition frequencies for13CCS and C13CS are analyzed simultaneously with millimeter-wave data, and the hyperfine interaction constants for both species are determined accurately. Astronomical implications for these radicals are discussed.

Hyperfine structure studies of Tantalum

A narrow bandwidth ring dye laser pumped by an argon ion laser has been used to investigate the hyperfine structure of the even and odd parity levels of tantalum by optogalvanic spectroscopy in the wavelength range 5640 to 6050 A. Seventeen transitions have been observed and eight of these have not been reported in the literature so far. These transitions involve 27 levels with 15 odd and 12 even parity configurations. The magnetic dipole hyperfine interaction constants A and the electric quadrupole interaction constants B for these levels have been computed and compared with the data available in literature. The results for the levels at 34799.71 cm−1, 26960.46 cm−1 and 19657.78 cm−1 are reported for the first time.

Nuclear quadrupole moment of scandium

The multiconfiguration Dirac-Fock model is employed to evaluate the effects of relativity and electron correlation on the hyperfine interaction constants of the 3${d}^{2}$ ${}^{3}{F}_{3}$, ${}^{3}{F}_{4}$, ${}^{1}{G}_{4}$, and $3d4p$ ${}^{3}{F}_{4}$ levels of Sc II. 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 substitutions from the 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. The calculated electric quadrupole hyperfine constants, together with previously computed values for other levels of Sc II, are used to evaluate the nuclear electric quadrupole moment of isotope 45 of scandium, for which the value $Q=\ensuremath{-}0.231(4)$ b is found.

ESR study of radical adducts of dialkoxyphosphoryl radicals with (η2-C60)lrH(CO)(PPh3)2 and (η2-C60IrH(8H12)(PPh3)

The reaction of phosphoryl radicals with (η2-C60)lrH(CO)(PPh3)2 and (η2-C60IrH(8H12)(PPh3) was shown (ESR) to result in the formation of isomers differing in the constants of hyperfine interaction (HFI) with31P nuclei,g-factors, and linewidths. It is likely that the addition of phosphoryl radicals at a distance of two-three bond lengths from the metallofragment is predominant.

Fine-structure analysis of the (5d+6s) $^5$ levels of Ta I

The fine structure of the prominent even levels of the neutral tantalum atom has been analyzed by simultaneous parametrization of one- and two-body interactions for the model space (5d+6s)5. The analysis was stimulated by the current discovery of several energy levels. It was possible to clear the configurations and designations of the energy levels given in commonly used tables. Magnetic-dipole hyperfine interaction constants A and electric-quadrupole hyperfine interaction constants B were calculated using the calculated eigenfunctions and adjusting radial integrals in a least-squares procedure which compares the calculated Aand B-constants with the experimental values. The rms error of this fitting procedure confirms the quality of the fine structure analysis. Moreover, wavenumbers and hyperfine constants of 52 further levels, up to now unidentified, are predicted.

Electron paramagnetic resonance of scandium in silicon carbide

The EPR spectra of scandium acceptors and Sc2+(3d) ions are observed in 6H-SiC crystals containing a scandium impurity. The EPR spectra of scandium acceptors are characterized by comparatively small hyperfine interaction constants, whose values are consistent with the constants for other group III elements in SiC: boron, aluminum, and gallium acceptors. The EPR spectra of scandium acceptors undergo major changes in the temperature interval 20–30 K. In the low-temperature phase the EPR spectra are characterized by orthorhombic symmetry, whereas the high-temperature phase has higher axial symmetry. The EPR spectra observed at temperatures above 35 K and ascribed by the authors to Sc2+(3d) ions, or to the A2− state of scandium, have significantly larger hyperfine structure constants and narrower lines in comparison with the EPR spectra of scandium acceptors. The parameters of these EPR spectra are close to those of Sc2+(3d) in ionic crystals and ZnS, whereas the parameters of the EPR spectra of scandium acceptors correspond more closely to the parameters of holes localized at group III atoms, in particular, at scandium atoms in GeO2. It is concluded that in all centers the scandium atoms occupy silicon sites.

The Rotational Spectrum of SH and SD

With the Cologne terahertz spectrometer, the lower J rotational spectrum of the SD radical has been detected for the first time in the laboratory, in analogy with our previous recent detection of the SH radical. The radicals were produced by discharging H2S (D2S) buffered with He and H2 (D2). The spectra were analyzed employing Hund's case (a) coupling scheme. The SH radical has an inverted 2Π state, as does OH, so that the 2Π3/2 state is the energetically lower one. For both SH and SD, the rotational and centrifugal distortion constants, the spin orbit, the spin rotation, the Λ-doublet, and the hyperfine interaction constants were determined by combining the newly acquired experimental data with those available in the literature. The rotational constant B0 for SD is 146885.297 (26) MHz, while our latest value for SH is 283587.62 (12) MHz (the values in parentheses denote the calculated uncertainty obtained by a least-squares fit). The SH radical and its deuterated isotopomer may be detectable in interstellar space because of the high cosmic abundance of elemental sulfur and the high abundance of HS. Since the 2Π1/2 electronic state lies nearly 400 cm–1 above the 2Π3/2 state, the rotational transitions in the 2Π1/2 state should only be detectable in hot interstellar sources, and they are potentially good indicators of star formation.

Electron Paramagnetic Resonance of Nd3+ and Ce3+ Impurities in PbWO4 Single Crystals

An EPR investigation of rare earth trace impurities in PbWO 4 single crystals was carried out at 4.2 < T < 300 K. The Nd 3+ and Ce 3+ ions were identified, being described by an axial spin Hamiltonian with an effective spin. The g-factors of Nd 3+ and Ce 3+ as well as the constants of hyperfine interaction of Nd 3+ were obtained.

Nitrogen in diamond thin films

The local structure, dynamical properties and spin-lattice relaxation rate of nitrogen in diamond films produced by plasma-assisted chemical vapor deposition has been investigated by electron spin resonance in the temperature range 10–773 K. We find an isotropic g-value g = 2.0024 and hyperfine interaction constants A ‖ = 40.7 G and A ⊥ = 28.2 G consistent with an axial distortion along one of the four equivalent [111] directions. The peak to peak line width is ΔH pp = 3.0 G and the spin concentration is of the order of N s = 9 × 10 18 cm −3. The line shape has Lorentzian character in the center and Gaussian character in the wings. The high-temperature reorientation frequency was found to follow an Arrhenius-type behavior with ν 0 = 3.2 × 10 12 Hz and E JT = 0.69 eV. From the saturation behavior of the resonance line the spin-lattice relaxation time was found to be of the order to T 1e ≈ 1.0 × 10 −5 s at room temperature and T 1e ≈ 1.0 × 10 −3 s at 10 K.

Measurements of the Syperfine Structure of Atomic Energy Levels in Co I

Most of the Co I lines recorded by high-resolution Fourier Transform Spectrometry in the region 3000–45000 cm−1 (30000–2222 A) show significant hyperfine Structure. Computer fits to 1020 of these line profiles have yielded values of the magnetic dipole hyperfine interaction constant A for 297 energy levels with an uncertainty of between 0.2% and 3%. The A Factors range from −0.0236 to +0.0598 cm−1 for the even levels, and from −0.03387 to +0.1028 cm−1 for the odd levels. For 208 of these A factors no previous measurements are known. Approximate values of the electric quadrupole hyperfine interaction constant B were found for 156 levels. These measurements of A and B factors allow, for the first time, correct allowance to be made for the effects of hyperfine structure in Co I both for abundance analysis and in the resolution of blended lines.

Location of muonium and hydrogen in C60 fullerene and associated electronic structure and hyperfine properties

The unrestricted Hartree-Fock (UHF) procedure is used to investigate the locations, associated electronic structures and hyperfine interactions for muonium and hydrogen in C60 fullerene. Our results indicate that from total energy considerations, in keeping with earlier investigations, the exohedral model has the lowest energy. However, the energies of the endohedral model involving the muonium (hydrogen) inside the fullerene and bonded to one of the carbon atoms, and of the muon at the center are found to be almost equal, contrary to earlier results. The hyperfine interaction constant for the endohedral site is in good agreement with that required to explain the lower observed muon spin-rotation (μSR) frequency in the C60-muonium system. The same appears to be the case for the exohedral model. However, there seems to be some uncertainty about the theoretical result in the latter case due to significant admixtures of higher spin states in the UHF wave-function. Additionally, in solid fullerene, the calculated location of the muonium for the exohedral model is such that it could be bonded to two fullerene molecules and therefore a muonium attached to a simple fullerene may not be representative of the exohedral state. This feature as well as the difficulty for the exohedral model of explaining the observed equality of the correlation times for relaxation effects associated with both μSR and13C relaxation times in nuclear magnetic resonance (NMR) experiments suggests that the endohedral model for muonium cannot at present be ruled out as a viable model in favor of the exohedral model. Possible avenues for future investigations to resolve some of the problems for both exohedral and endohedral models are discussed. Results obtained for muonium at the center of fullerene are presented and compared to the features of the observed high frequency μSR signal, and possible improvements in theory are discussed.

Rotational spectra, structures, and dynamics of small Arm–(H2O)n clusters: The Ar2–H2O trimer

Rotational spectra have been observed for the Ar2–H2O trimer and several of its isotopomers with the Balle/Flygare pulsed nozzle, Fourier transform microwave spectrometer. Analysis gives a planar T-shaped structure with C2v symmetry and the bidentate protons pointed at the argons. Two sets of asymmetric top transitions were found for the species with H2O, D2O, or H2 18O. Several lines of evidence support assigning them to internal rotor states of the water, the upper set to Σ(000) and the lower to Σ(101) as in the Ar–H2O dimer. Support includes: Hyperfine interaction constants which differ for the two states of water; Systematic aspects of the rotational constants such as B’s that are little affected by isotopic substitution; and MMC calculations which indicate the importance of rovibrational coupling. The Ar–Ar distance for the Σ(000) state of the trimer is estimated to be 3.822 Å and the center of mass (Ar2) to center of mass (H2O) distance to be 3.173 Å. An intriguing result is finding the hyperfine interaction constants of the water in the trimer to be very nearly the same as those reported earlier for the dimer. This shows the two dynamic states of the water are the same in the dimer and trimer, as is the average projection of the water C2 axis onto the inertial frame.