Fermi Contact Parameter Research Articles

Optical, structural, physical, and nuclear shielding properties, and albedo parameters of TeO2–BaO–B2O3–PbO–V2O5 glasses

In this study, glass systems were constructed according to the formula 34TeO2∙xBaO∙35B2O3∙(30-x)PbO∙1V2O5 (x=0, 5, 10, 15, 20, 30 mol%). The gamma, neutron, proton, and alpha shielding characteristics of the glasses were evaluated for nuclear security applications. The mass attenuation coefficient (MAC), half-value layer, mean free path, effective atomic number, and radiation protection efficiency (RPE) were experimentally measured in the energy range of 59.54–661.62 keV. In addition, the theoretical MAC values were determined. The exposure buildup factor, fast neutron removal cross section, mass stopping power, and projected range values for proton (H1) and alpha (He+2) particles were theoretically determined. Albedo parameters were measured for the prepared glasses at photon energy of 59.54 keV. The optical and structural properties were studied using X-ray diffraction, FT-IR Fourier transform infrared, ultraviolet–visible, and electron paramagnetic resonance spectroscopy. The glass samples comprised structural units such as TeO4, TeO3, BO3, and BO4. The spin Hamiltonian parameters, g∥, g⊥, A∥, A⊥, dipolar hyperfine coupling parameter, P, and Fermi contact parameter, κ, were calculated. The molecular orbital parameters, α2, β2, and γ2, were determined by optical absorption spectroscopy. The number of bonds per unit volume in the glasses ranged between 8.763 and 9.212×1028 m−3. The most reflective compound among the glasses investigated was BaO. Good agreement was found between the theoretical and experimental MAC values. TeBaBPbV1 glass was identified as a potential candidate for use in neutron, gamma, proton, and alpha shielding.

Level structure of deeply bound levels of the c3Σg+ state of Rb287

We spectroscopically investigate the hyperfine, rotational and Zeeman structure of the vibrational levels $\text{v}'=0$, $7$, $13$ within the electronically excited $c^3\Sigma_g^+$ state of $^{87}\text{Rb}_2$ for magnetic fields of up to $1000\,\text{G}$. As spectroscopic methods we use short-range photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold molecules which have been previously prepared in several well-defined quantum states of the $a^3\Sigma_u^+$ potential. As a byproduct, we present optical two-photon transfer of weakly bound Feshbach molecules into $a^3\Sigma_u^+$, $\text{v}=0$ levels featuring different nuclear spin quantum numbers. A simple model reproduces well the molecular level structures of the $c^3\Sigma_g^+$ vibrational states and provides a consistent assignment of the measured resonance lines. Furthermore, the model can be used to predict the relative transition strengths of the lines. From fits to the data we extract for each vibrational level the rotational constant, the effective spin-spin interaction constant, as well as the Fermi contact parameter and (for the first time) the anisotropic hyperfine constant. In an alternative approach, we perform coupled-channel calculations where we fit the relevant potential energy curves, spin-orbit interactions and hyperfine functions. The calculations reproduce the measured hyperfine level term frequencies with an average uncertainty of $\pm9\:$MHz, similar as for the simple model. From these fits we obtain a section of the potential energy curve for the $c^3\Sigma_g^+$ state which can be used for predicting the level structure for the vibrational manifold $\text{v}'=0$ to $13$ of this electronic state.

Terahertz Spectroscopy of 25MgH (X2Σ+) and 67ZnH (X2Σ+): Bonding in Simple Metal Hydrides

Pure rotational spectra of (25)MgH (X(2)Σ(+)) and (67)ZnH (X(2)Σ(+)) were recorded using direct absorption techniques. These free radicals were synthesized by the reaction of metal vapor, generated in a Broida-type oven, with H2 in a dc discharge. The N = 0 → 1 and N = 1 → 2 transitions were recorded for both species in the frequency range 342-789 GHz. Spin-rotation and metal and proton hyperfine interactions were resolved in the spectra. From these data, rotational, fine structure, and hyperfine constants were determined, including the Fermi contact, dipolar, and electric quadrupole parameters of the (25)Mg and (67)Zn nuclei. Comparison of the metal and proton hyperfine terms suggests that the unpaired electron resides in a σ molecular orbital that has significant s contributions from both the metal and the hydrogen atoms. The dipolar terms for both metals are relatively large, in contrast to those of the proton, and indicate spσ and possibly sdσ (zinc only) orbital hybridization. The quadrupole constants arise principally from the p/d orbital character of the unpaired electron, although there is a non-negligible polarization contribution. These results suggest significant covalent character in both MgH and ZnH, in contrast to their fluoride analogs.

Communication: Electric dipole moment and hyperfine interaction of tungsten monocarbide, WC

The [17.6]2← X(3)Δ(1)(1,0) band of tungsten monocarbide, WC, was recorded using laser induced fluorescence both field-free and in the presence of a static electric field. The Stark induced shifts of the R(1) and Q(2) lines were analyzed to produce values for the permanent electric dipole moments, μ, of 3.90 ± 0.04 D and 2.57 ± 0.04 D for the X(3)Δ(1)(v = 0) and [17.6]2(v = 1) states, respectively. An upper limit to the Ω-doubling parameter, õ(Δ), of 2 MHz is established. The (183)W(I = 1/2) Fermi contact parameter, b(F), for the X(3)Δ(1)(v = 0) is estimated to be 1363 MHz. The results are compared with theoretical predictions and a molecular orbital correlation description.

Electron Spin Resonance and Ground State Wave Functions of Vanadyl Ion in LiNaSO4

Electron spin resonance (ESR) of VO2+ doped into LiNaSO4 has been studied at 300 K on an X-band spectrometer. The ESR powder spectra have been analyzed and spin Hamiltonian parameters have been evaluated. Using the crystal-field approach, a theoretical estimate of the ground state wave functions of VO2+ in LiMSO4 (M = Na, K) has been made from the ESR data. The dipolar hyperfine coupling constant P and Fermi contact parameter K have also been estimated.

Resonant two-photon ionization spectroscopy of jet-cooled tantalum carbide, TaC

The optical spectrum of diatomic TaC has been investigated for the first time, with transitions recorded in the range from 17,850 to 20,000 cm(-1). Six bands were rotationally resolved and analyzed to obtain ground and excited state parameters, including band origins, upper and lower state rotational constants and bond lengths, Fermi contact parameter b(F) for the ground state, and lambda doubling parameters for the excited states. The ground state of TaC was found to be X (2)Sigma(+), originating from the 1sigma(2)2sigma(2)1pi(4)3sigma(1) electronic configuration, in which only the valence orbitals arising from the Ta(5d+6s) and C(2s+2p) orbitals are listed. All of the rotationally resolved and analyzed bands were found to originate from the ground state, giving B(0)"=0.489 683(83) cm(-1), r(0)"=1.749 01(15) A, and b(F)"=0.131 20(36) cm(-1) (1sigma error limits) for (181)Ta (12)C. Comparison of the Fermi contact parameter to the atomic value shows that the 3sigma orbital is approximately 75% Ta 6s in character. The other group 5 transition metal carbides, VC and NbC, have long been known to have 1sigma(2)2sigma(2)1pi(4)1delta(1), (2)Delta ground states, with low-lying 1sigma(2)2sigma(2)1pi(4)3sigma(1), (2)Sigma(+) excited states. The emergence of a different ground state in TaC, as compared to VC and NbC, is due to the relativistic stabilization of the 6s orbital in Ta. This lowers the energy of the 6s-like 3sigma orbital in TaC, causing the 1sigma(2)2sigma(2)1pi(4)3sigma(1), (2)Sigma(+) state to fall below the 1sigma(2)2sigma(2)1pi(4)1delta(1), (2)Delta state.

Heavy atom nitroxyl radicals. II: Spectroscopic detection of H2As=O, the prototypical arsenyl free radical

The previously unknown arsenyl (H(2)AsO) free radical has been identified in the gas phase through a combination of laser-induced fluorescence and single vibronic level emission spectroscopy in a supersonic expansion. Three isotopologues, H(2)AsO, HDAsO, and D(2)AsO have been detected as products of an electric discharge in mixtures of arsine or deuterated arsines, CO(2), and argon. The observed spectra are assigned as due to the B (2)A(')-X (2)A(') electronic transition in which an electron in the ground state pi orbital is promoted to the pi( *) orbital. Rotational analysis of high-resolution spectra proves that the radical is nonplanar in both electronic states with the following r(0) structures: r(")(As-H)=1.513(4) A, r(")(As-O)=1.672(1) A, theta(")(HAsH)=101.8(4) degrees , ground state out-of-plane angle=63.1 degrees ; r(')(As-H)=1.525(10) A, r(')(As-O)=1.806(3) A, theta(')(HAsH)=93.4(10) degrees , and excited state out-of-plane angle=70.7 degrees . Small hyperfine splittings in the spectra have enabled the determination of the arsenic Fermi contact parameter in both states. The results of our ab initio studies of the ground and excited state of this radical (see immediately preceding paper) are in good agreement with the spectroscopic analysis.

The hyperfine interaction in the AΠ1∕22 and XΣ+2 states of ytterbium monofluoride

The fine and hyperfine interaction parameters in the A (2)Pi(1/2)(v=0) and X (2)Sigma(+)(v=0) states of the odd metal nuclear spin isotopologues of ytterbium monofluoride, (171)YbF and (173)YbF, have been determined from an analysis of high-resolution laser induced fluorescence spectra of the A (2)Pi(12)<--X (2)Sigma(+)(0,0) band. The observed ground X (2)Sigma(+)(v=0) state (171)Yb(I=1/2) Fermi contact parameter is significantly smaller than that determined from the matrix isolation electron spin resonance measurement [Van Zee et al., J. Phys. Chem. 82, 1192 (1978)]. An interpretation of the (173,171)Yb magnetic hyperfine and nuclear electric quadrupole coupling parameters is given.

Microwave spectra of O2–HF and O2–DF: Hyperfine interactions and global fitting with infrared data

Spectra of the open shell complexes O(2)-HF and O(2)-DF were recorded using Fourier transform microwave spectroscopy. A complete analysis of the hyperfine structure and a global fit including microwave and infrared frequencies [W. M. Fawzy, C. M. Lovejoy, D. J. Nesbitt, and J. T. Hougen, J. Chem. Phys. 117, 693 (2002)] are reported. The Fermi contact interaction between the electron and nuclear spins, the electron spin-nuclear spin dipolar interaction, the nuclear spin-nuclear spin dipolar interaction, and the nuclear electric quadrupole interaction (for O(2)-DF) were considered in the analysis. The correspondence between the magnetic hyperfine constants and the two nuclei of the H(D)F is unambiguously established. In both O(2)-HF and O(2)-DF, the Fermi contact parameter is larger for the fluorine than for the hydrogen, while for the nuclear spin-electron spin dipolar hyperfine constants, the reverse is true. The effective angle between the HF bond and the a axis of the complex, determined from the nuclear spin-nuclear spin interaction constant, is 38(4) degrees. The same angle for the DF complex, derived from the deuterium nuclear quadrupole coupling constant, is 31(4) degrees.

Electronic spectroscopy of jet-cooled HCP+: Molecular structure, phosphorus hyperfine structure, and Renner-Teller analysis

Laser-induced fluorescence spectra of jet-cooled HCP(+) and DCP(+) have been obtained with the pulsed discharge technique using HCPDCP and argon precursor mixtures. Transitions involving all of the excited state vibrations have been observed and a set of vibrational constants has been obtained. High-resolution spectra of the (2)Pi(32) components of the 0(0) (0) bands of both isotopomers have been recorded, and these spectra show resolved phosphorus hyperfine structure which allowed the determination of the excited state Fermi contact parameter. The B values were used to obtain the ground and excited state effective geometric parameters as r(0) (")(CH)=1.077(2) A, r(0) (")(CP)=1.6013(3) A, r(0) (')(CH)=1.082(2) A, and r(0) (')(CP)=1.5331(3) A. A Renner-Teller analysis of the ground state vibrational energy levels obtained from the literature was attempted. All of the observed levels of DCP(+) and the majority of those of HCP(+) were satisfactorily fitted with a standard Renner-Teller model, but three HCP(+) levels showed large systematic deviations which could not be accommodated by reassignments or improvements in the Fermi resonance Hamiltonian. Further improvements in the theory or in the experimental data will be needed to resolve this discrepancy.

High resolution laser induced fluorescence spectroscopy of the [18.8]Φi3−XΦi3 (0,0) band of cobalt monofluoride

The fine and hyperfine interaction parameters in the [18.8] (3)Phi (upsilon=0) and X (3)Phi (upsilon=0) states of cobalt monofluoride, CoF, have been determined from an analysis of high-resolution laser induced fluorescence spectra of the [18.8] (3)Phi(3)-X (3)Phi(3) and [18.8] (3)Phi(4)-X (3)Phi(4) band systems. The previously reported pure rotational transitions of the X (3)Phi(4)(upsilon=0) state [T. Okabayashi and M. Tanimoto, J. Mol. Spectrosc. 221, 149 (2003)] were included in the data set. The hyperfine parameters for (59)Co (I=72) and (19)F (I=12) have been interpreted using atomic data together with a proposed molecular orbital description for the [18.8](3)Phi(i) and X (3)Phi(i) states. A comparison of the hyperfine parameters in the X (3)Phi state of cobalt monohydride, CoH, with those of the X (3)Phi state of CoF reveals that the bonding in the two molecules is significantly different. It is shown that, in a situation where the Omega substates of a multiplet degenerate electronic state are analyzed separately, the Fermi contact parameter b can be determined with fair accuracy from the apparent centrifugal distortion of the hyperfine structure.

EPR of vanadyl impurity in zinc ammonium trihydrogen bis(orthophosphate) monohydrate single crystal

The electron paramagnetic resonance spectroscopic investigation of VO(II)-doped zinc ammonium trihydrogen bis(orthophosphate) monohydrate single crystal has been carried out at 300 K. The single crystal, rotated along the three orthogonally crystallographic axes, have yielded spin Hamiltonian parameters g and A as: g xx = 1.978, g yy = 1.974, g zz = 1.925 and A xx = 7.4, A yy = 7.8, A zz = 19.4 mT. These spin Hamiltonian parameters reflect a slight deviation from axially symmetry to rhombic, which is elucidated by the interstitial occupation of the vanadyl ion. The isofrequency plots and EPR spectra at few orientations have been simulated using the calculated spin Hamiltonian parameters. The Fermi contact parameter ( κ) and dipolar interaction parameter ( P) have been calculated as 0.857 and −128 × 10 −4 cm −1, respectively. The percentage of metal oxygen bond has been identified as 20%.

Nuclear hyperfine structure in the X3Σ + state of 91ZrC

Electronic band systems of zirconium monocarbide, ZrC, in the 16 000–19 000 cm −1 region have been observed following the reaction of laser-ablated Zr atoms with methane under supersonic free-jet conditions. Rotational analyses of high-resolution spectra have shown that the ground state of ZrC is a 3Σ state, with r 0=1.8066 Å and an unexpectedly small spin–spin parameter, λ=0.5139 cm −1. The spectra are dense because of the five naturally occurring isotopes of Zr. Four of these, with mass numbers 90, 92, 94, and 96, have I=0, but the fifth, 91Zr, present in 11.22% abundance, has I=5/2. Lines of 91ZrC can be assigned in some of the strongest bands, and are found to display sizeable hyperfine splittings, with widths of up to 0.2 cm −1. Analysis shows that the largest hyperfine effects are in the ground state, where b=−0.03133±0.00015 cm −1 and c=−0.00123±0.00037 cm −1 (3 σ error limits). The large Fermi contact parameter, b, indicates that an unpaired Zr 5 sσ electron is present, which, taken together with the small value of λ, means that the ground state must be a 3Σ + state, from the electron configuration (Zr 5 sσ) 1 (C 2 pσ) 1. Internal hyperfine perturbations occur between the F 1 and F 3 electron spin components of the ground state in the range N=2–4, producing extra lines in some of the branches; the perturbations are of the type Δ N=0, Δ J=±2, and are a second-order effect arising because the F 1 ( J= N+1) and F 3 ( J= N−1) spin components both interact with the F 2 ( J= N) component through Δ N=0, Δ J=±1 matrix elements of the Fermi contact operator. Second-order perturbations of this type can only occur in states that are very close to case ( b) coupling.

Rotational and hyperfine analysis of the near infrared Φ43–X 3Φ4 transitions of CoCl and CoI

Electronic transitions of cobalt monochloride and cobalt monoiodide have been studied using laser vaporization–reaction free jet expansion and laser induced fluorescence spectroscopy in the near infrared region. The observed transitions have been identified as the [10.3] Φ43–X 3Φ4 transition of CoCl and [11.0] Φ43–X 3Φ4 transition of CoI. The magnetic hyperfine structure arising from the cobalt nucleus with I=7/2 was resolved and analyzed. Accurate rotational and hyperfine parameters for the [10.3] Φ43 and X 3Φ4 states of CoCl and [11.0] Φ43 and X 3Φ4 states of CoI have been obtained. Comparison of Fermi contact parameters, bF, for the upper states indicated that the observed [10.3] Φ43–X 3Φ4 transition of CoCl and [11.0] Φ43–X 3Φ4 transition of CoI have arisen from the promotion of an electron from the bonding σ orbital to a slightly antibonding σ orbital. Observed low-lying Φ3 states of the cobalt monohalides and hydride are also compared and discussed.

Laser spectroscopy of VS: hyperfine and rotational structure of the C4Σ −– X4Σ − transition

The (0,0) and (0,1) bands of the C 4Σ −– X 4Σ − electronic transition of VS (near 809 and 846 nm, respectively) have been recorded at high resolution by laser-induced fluorescence, following the reaction of laser-ablated vanadium atoms with CS 2 under supersonic free-jet conditions. A least squares fit to the resolved hyperfine components of the rotational lines gives the rotational constants and bond lengths as C 4Σ −: B 0=0.188898±0.000027 cm −1 , r 0=2.1315 A ̊ ; X 4Σ −: B 0=0.203684±0.000025 cm −1 , r 0=2.0526 A ̊ . The electron spin parameters for the two states show that there are some similarities between the states of VS and those of VO, but the hyperfine parameters show that the compositions of the partly filled molecular orbitals are by no means the same. The ground state Fermi contact parameter of VS, b( X 4Σ −), is only 58% of that of the ground state of VO, which implies that the σ orbital of the ground σδ 2 electron configuration has less than 50% vanadium 4 s character. Similarly, the excited state Fermi contact parameter, b( C 4Σ −), is very much smaller than that of VO. No local rotational perturbations have been found in the C 4Σ − state of VS, though an internal hyperfine perturbation between the F 2 and F 3 electron components at low N confuses the hyperfine structure and induces some forbidden (Δ J=±2) rotational branches.

Determination of the electric dipole moment and excited state Fermi contact parameter of the GeCH radical

The germanium methylidyne (GeCH) radical has been studied at high resolution by laser-induced fluorescence spectroscopy in a skimmed molecular beam. The radical was produced in a pulsed discharge jet source using methyltrichlorogermane as the precursor. Single rotational lines of the à 2Σ+–X̃ 2Π3/2 component of the 000 band at 14 070 cm−1 were recorded with linewidths of 35 MHz, showing resolved proton magnetic hyperfine splittings. The observed hyperfine splittings of 12 rotational lines were satisfactorily modeled by varying a single upper state Fermi contact parameter, giving bF=163(2) MHz. Optical Stark measurements were performed on the GeCH74 P11(3/2)F′=1 hyperfine transition and the permanent electric dipole moments determined to be μ(X̃ 2Π)=0.122(2) D and μ(à 2Σ+)=1.29(2) D. Our ab initio predictions of the dipole moments and excited state Fermi contact parameter are in fair agreement with experiment. The magnitudes of the determined parameters are discussed based on the molecular orbitals and compared to similar measurements on SiCH.

Polarizabilities and other properties of the tdµ molecular ion

Wave functions of the Hylleraas type were used earlier to calculate energy levels of muonic systems. Recently, we found in the case of the molecular ions H2+, D2+, and HD+ that it was necessary to include high powers of the internuclear distance in the Hylleraas functions to localize the nuclear motion when treating the ions as three-body systems without invoking the Born–Oppenheimer approximation. We tried the same approach in a muonic system, tdµ– (triton, deuteron, and muon). Improved convergence was obtained for J = 0 and 1 states for shorter expansions when we used this type of generalized Hylleraas function, but as the expansion length increased the high powers were no longer useful. We obtained good energy values for the two lowest J = 0 and 1 states and compared them with the best earlier calculations. Expectation values were obtained for various operators, the Fermi contact parameters, and the permanent quadrupole moment. The cusp conditions were also calculated. The polarizability of the ground state was then calculated using second-order perturbation theory with intermediate J = 1 pseudostates. (It should be possible to measure the polarizability by observing Rydberg states of atoms with tdµ– acting as the nucleus.) In addition, the initial sticking probability (an essential quantity in the analysis of muon catalyzed fusion) was calculated and compared with earlier results. PACS Nos.: 30.00, 36.10-k, 02.70-c

Hyperfine structure and the Stark effect in the electronic spectrum of the SiCH radical with implications for microwave spectroscopy and radioastronomy

A skimmed molecular beam of silicon methylidyne, SiCH, was produced using a pulsed discharge jet source with methyltrichlorosilane as the precursor. Linewidths of 35 MHz were achieved using laser-induced fluorescence detection. The field-free fine and magnetic hyperfine interactions and Stark effects were analyzed for the à 2Σ+-X̃ 2Π3/2 component of the 301 band at 12 934.428 cm−1. The observed proton hyperfine structure was satisfactorily reproduced with a single upper state Fermi contact parameter bF=117(2) MHz. The determined permanent electric dipole moments are μ(à 2Σ+)=1.51(2) D and μ(X̃ 2Π3/2)=0.066(2) D. Our ab initio predictions of the Fermi contact parameter and dipole moments at the B3LYP and quadratic configuration interaction including single and double substitutions levels of theory are in reasonable accord with experiment. An interpretation of the magnitudes of the determined parameters is given based on the highest occupied molecular orbitals. The very small ground state dipole moment will make microwave and radioastronomy studies of SiCH very challenging.

Static properties and the Stark effect of the ground state of the HD molecular ion

We have calculated static properties of the ground state of the HD(+) ion and its lowest-lying P-state without making use of the Born-Oppenheimer approximation, as was done in the case of H2(+) and D2(+) [Phys. Rev. A 58, 2787 (1998)]. The ion is treated as a three-body system whose ground state is spherically symmetric. The wavefunction is of generalized Hylleraas type, but it is necessary to include high powers of the internuclear distance to localize the nuclear motion. We obtain good values of the energies of the ground S-state and lowest P-state and compare them with earlier calculations. Expectation values are obtained for various operators, the Fermi contact parameters, and the permanent quadrupole moment. The cusp conditions are also calculated. The polarizability was then calculated using second-order perturbation theory with intermediate P pseudostates. Since the nuclei in HD(+) are not of equal mass there is dipole coupling between the lowest two rotational states, which are almost degenerate. This situation is carefully analyzed, and the Stark shift is calculated variationally as a function of the applied electric field.

Hyperfine anomaly for the ground state of 9 Be

The Fermi contact parameter which represents hyperfine structure (hfs) has been accurately calculated for the ground state of the 9Be+ ion in a previous paper. In the present paper, the calculated parameter is compared with a high precision measurement to derive the hfs anomaly (the Bohr-Weisskopf effect), which is caused by nuclear magnetization distribution. The obtained hfs anomaly shows a satisfactory agreement with the result of a nuclear shell model calculation.