Electric Quadrupole Coupling Constants Research Articles

Rotational spectroscopy of AuH and AuD in the 1Σ + electronic ground state

The rotational transitions of AuH and AuD with the hyperfine structure due to the gold nucleus ( I = 3/2) were observed in the 220, 430, and 650 GHz regions with source modulation microwave spectrometers. The AuH and AuD molecules were generated by sputtering from a gold sheet lining the inner surface of a stainless-steel cathode in a dc glow discharge through hydrogen and deuterium gases, respectively, diluted with argon gas. The nuclear electric quadrupole coupling constant and the nuclear magnetic spin-rotation coupling constant were determined for each isotopomer by a least-squares analysis.

Precise Nuclear Quadrupole Moments of 8B and 13B

The electric quadrupole coupling constants eqQ/h of 8B (I π = 2+, T 1/2 = 769 ms) and 13B (I π = 3/2−, T 1/2 = 17.4 ms) in single crystal TiO2 have been precisely measured by the β-NQR technique. The ratios of these Q moments to Q(12B) were determined as |Q(8B)/Q(12B)| = 4.882(32) and |Q(13B)/Q(12B)| = 2.768(24).

Production of Nuclear Polarization of Na Isotopes at ISAC/TRIUMF and its Hyperfine Interaction

Hyperfine interactions of Na isotopes in single crystals have been studied using highly nuclear polarized 20,21,26,27,28Na beams provided by ISAC/TRIUMF. The degree of polarization kept in the crystals, the spin-lattice relaxation times, the electric quadrupole coupling constants and the initial distribution of the populations were measured. Such knowledge is indispensable for the application of the hyperfine interactions in the study of precision measurements such as the nuclear structure through nuclear moments and the fundamental symmetries.

Quadrupole Moments of Na Isotopes

The electric quadrupole coupling constants eqQ/h of 20Na (Iπ = 2+, T 1/2 = 449.7 ms), 21Na (Iπ = 3/2, T 1/2 = 22.49 s) and 25Na (Iπ = 5/2, T 1/2 = 59.6 s) in single crystal ZnO and TiO2 were precisely measured by applying the β-NMR technique. The ratio of the quadrupole moments between 20Na (25Na) and 21Na was determined to be 0.728 ± 0.023 (0.011 ± 0.002).

The permanent electric dipole moments of WN and ReN and nuclear quadrupole interaction in ReN

The high-resolution laser induced fluorescence spectra of tungsten mononitride WN and rhenium mononitride ReN have been recorded in a laser ablation/molecular beam spectrometer. The field free spectrum of the (0,0)A (4)Pi(3/2)-X (4)Sigma(1/2) (-) band system of (186)WN has been analyzed to produce B("), B('), and gamma(") values of 0.4659(2), 0.4554(2), and 0.0518(1) cm(-1), respectively. The permanent electric dipole moments mu for the X (4)Sigma(1/2) (-) and A (4)Pi(3/2) state were determined to be 3.77(18) and 2.45(3) D, respectively, from the analysis of the optical Stark effect. The (0,0)[26.0]0(+)-X0(+) band system of ReN was recorded in the presence of a variable static electric field. The ground and excited state electric dipole moments of (187)ReN were determined to be mu(X0(+))=1.96(8) D and mu([26.0]0(+))=3.53(4) D. Splittings in the field free (187)ReN spectrum were analyzed to produce (187)Re (I=5/2) nuclear electric quadrupole coupling constants e(2)Qq(0) of -0.0304(8) and 0.0328(9) cm(-1) for the X0(+) and [26.0]0(+) states, respectively. A molecular orbital correlation model is used to interpret the observation and a comparison is made to CrN and MoN.

155Gd Mössbauer spectroscopic and X-ray diffraction study of the Zr 1− xGd xO 2− x/2 (0< x≤1.0) system

155Gd Mössbauer spectroscopy has been applied for the Gd x Zr 1− x O 2− x/2 system, to elucidate the local structure around the Gd 3+ over the entire 0< x≤1.0 range. Powder X-ray diffraction (XRD) measurements showed that below 1550 °C an intermediate pyrochlore (P) phase forms in the middle 0.45≤ x≤0.55 range, sandwitched with a disordered defect-fluorite (F) phase on both sides (0.18≤ x<0.45 and 0.55< x≤0.62), and upon heating above 1550 °C the former (P) is also disordered to the latter (F). 155Gd-Mössbauer spectra in the solid solution region (0.18≤ x≤0.62) apparently consisted of quadrupole split doublet which indicates the existence of one kind of distorted Gd site, in contrast to the well-resolved two doublets observed for the C-type Gd 2O 3 ( x=1.0). 155Gd-Mössbauer parameters in the solid solution region (0.18≤ x≤0.62) such as electric quadrupole coupling constant (e 2q Q), line width (2Γ) and relative absorption area (RAA) were found to exhibit a characteristic maximum around the ideal-pyrochlore composition ( x=0.50), while isomer shift ( δ) showed different behavior that this is nearly constant for 0.18≤ x≤0.50 and increases slightly for x>0.50. Their basic features were unchanged upon disordering above 1550 °C. These Mössbauer results suggest that the Gd x Zr 1− x O 2− x/2 solid solution (0.18≤ x≤0.62) has essentially a pyrochlore(P)-type local structure, whether long-range ordered or not, both the Gd–O bond strength and anisotropy attaining a maximum at x=0.50.

Zinc solid-state NMR spectroscopy of human carbonic anhydrase: implications for the enzymatic mechanism.

The pH dependence of the (67)Zn solid-state nuclear magnetic resonance spectroscopy of human carbonic anhydrase (CAII) has been investigated to characterize the nature of the fourth ligand. CAII, through the Zn(2+)-bound hydroxide, catalyzes the deceptively simple reaction: CO(2) + H(2)O <==> HCO(3)(-) + H(+). The accepted mechanism for CAII would predict that water would be bound to the Zn(2+) at pH 5 and hydroxide would be bound at pH 8.5. The measured values for the electric field gradient (EFG) or quadrupole coupling constant (Cq) for CAII are independent of pH within the limits of the experimental error, i.e., 9.8 +/- 0.2 MHz. The EFG interaction has been predicted by ab initio electronic structure calculations for water and hydroxide bound to the zinc, including various levels of hydrogen bonding. After comparing the predicted Cq's with the experimental values, we conclude that the species present from pH 5-8.5 is the hydroxide form. The NMR data presented here is not consistent with the accepted mechanism for CAII. We show that the NMR data is consistent with an alternative mechanism of CAII.

Measurement of hyperfine coupling constants of singly ionized rare earth ions

Hyperfine structure spectra of singly ionized rare earth ions were measured by collinear fast-ion-beam laser spectroscopy. Hyperfine structures in the range of 560–620 nm were well resolved. The magnetic dipole coupling constants and electric quadrupole coupling constants of the excited levels and metastable levels in 139La +, 141Pr +, 143,145Nd +, 151,153Eu +, and 159Tb + were determined.

Precise measurement of hyperfine structure in the $ \mathsf {5P_{3/2}}$ state of $ \mathsf {^{85}}$ Rb

We demonstrate a technique to measure hyperfine structure using a frequency-stabilized diode laser and an acousto-optic modulator locked to the frequency difference between two hyperfine peaks. We use this technique to measure hyperfine intervals in the 5 P 3/2 state of 85Rb and obtain a precision of 20 kHz. We extract values for the magnetic-dipole coupling constant A = 25.038(5) MHz and the electric-quadrupole coupling constant B = 26.011(22) MHz. These values are a significant improvement over previous results.

Rotational spectrum of [formula omitted] and [formula omitted]: completely resolved nuclear hyperfine structures due to [formula omitted] and [formula omitted

The pure rotational spectrum of 13 C 17 O has been observed in the millimeter- and submillimeter-wave region using the Lamb-dip technique in order to increase the instrumental resolving power and so to resolve both the hyperfine structure due to 17 O and that due to 13 C . In this way very accurate values of the rotational and centrifugal distortion constants, the 17 O nuclear electric quadrupole coupling constant and the 17 O and 13 C spin–rotation constants have been obtained. In addition, the J=1←0 and J=2←1 transitions of 13 C 18 O have been recorded using the Lamb-dip technique. The resolved hyperfine structure of these transitions allowed us to determine the rotational and 13 C spin–rotation constants. The experimental determination of all these parameters has been supported by ab initio computations.

Quantitative Comparison of REAPDOR and TRAPDOR Experiments by Numerical Simulations and Determination of H–Al Distances in Zeolites

Quantitative H–Al distances in acid sites of two zeolites with MFI and IFR framework topology were obtained by numerical simulation of 1H{27Al} rotational echo adiabatic passage double resonance (REAPDOR) experiments. A 27Al offset-dependent data set yields for each resolved 1H NMR line a corresponding nuclear electric quadrupole coupling constant of the neighboring 27Al site. This information is used for analyzing a second data set for on-resonance irradiation, where the dipolar evolution time (number of rotor cycles) was varied, to yield the 1H–27Al dipolar coupling constant. Numerical simulations indicate that the REAPDOR method does not depend significantly on the polar angles, defining the orientation of the electric field gradient tensor of 27Al with respect to the Al–H dipolar vector. In contrast, the transfer of populations in double resonance sequence is sensitive to these angles, and it can be thus used to measure them.

Submillimeter-Wave Spectra of H2Cl+ and its Isotopic Species: Molecular Structure

The rotational spectra of HD35Cl+, H235Cl+, and H237Cl+ were measured in the frequency region of 180 to 550 GHz with a source-modulated submillimeter-wave spectrometer. The ions were generated in a free space absorption cell by a hollow-cathode discharge in a gas mixture of Cl2 and He to which H2 and/or D2 was added. Precise molecular constants including the electric quadrupole coupling constants were determined for the three species. The zero-point average structure, rz, was calculated from moments of inertia corrected for harmonic terms. The harmonic force field of H2Cl+ was derived from previously estimated harmonic vibrational frequencies and inertial defects. The rz structures obtained are rz(Cl–H)=1.320 57(48)Å and θz(H–Cl–H)=94.238(72)° for H235Cl+ and rzCl–H)=1.320 60(38)Å and θz(H–Cl–H)=94.239(58)° for H237Cl+, where values in parentheses indicate errors due to residual inertial defects among the corrected moments of inertia. When the θz of HD35Cl+ is assumed to be the same as that of H235Cl+, the rz(Cl–H) and rz(Cl–D) lengths of HD35Cl+ are calculated to be 1.320 69(69) Å and 1.316 54(111) Å, respectively.

Density functional theory calculations of nuclear quadrupole coupling constants with calibrated 14N quadrupole moments

Density functional calculations of the electric field gradient tensor at the nitrogen nucleus in 13 test molecules, containing 14 nitrogen sites, have been performed using the linear combination of Gaussian-type orbital Kohn-Sham density functional theory (LCGTO-KSDFT) approach. Local and gradient corrected functionals were used for all-electron calculations. All the molecular structures were optimized at their respective levels of theory with extended basis sets. Calibrated 14N nuclear quadrupole moments were obtained through a fitting procedure between calculated electric field gradients and experimental nuclear quadrupole coupling constants of the test set of molecules for each basis set and functional considered. With these calibrated 14N nuclear quadrupole moments, the nuclear quadrupole coupling constants of the following selected systems were determined: fluoromethylisonitrile, pyridine, pyrrole, imadazole, pyrazole, 1,8-bis(dimethyl-amino)naphthalene, cyclotetramethylenetetranitramine, cocaine and heroin.

Measurement of hyperfine coupling constants of the excited states 4f 7 ( 8 S 0 7/2 )6p 3/2 (7/2, 3/2) in 151,153 Eu +

Hyperfine structure spectra of singly ionized europium have been measured by collinear fast-ion-beam laser spectroscopy. All the spectral lines were resolved and the magnetic dipole and electric quadrupole coupling constants of the metastable and excited levels were determined.

Rotational spectrum of the N 2··CO complex: ortho-N 2 and para-N 2

Pure rotational spectra of 14 N 2 ··CO, 15 N 14 N ··CO, and 15 N 2 ··CO have been observed using a Fourier transform microwave spectrometer. Two sets of transitions with J=2←1, 3←2, and 4←3 were observed for 14 N 2 ··CO and 15 N 2 ··CO; transitions with smaller effective rotational constants B were stronger than those with larger B for the 14 N 2 ··CO complex, while the opposite was observed for 15 N 2 ··CO. It was concluded that for 14 N 2 ··CO the first set corresponds to the K=0 stack of ortho-N 2 and the second to K=1 of para-N 2 based on a previous infrared analysis, hyperfine splittings, and the spin statistical weights. In the case of 15 N 14 N ··CO, only one set was observed because of the lack of symmetry. The electric quadrupole coupling constant of 14 N is much smaller, while the centrifugal distortion constant is much larger, than those of related complexes.

Hahn-echoes from [formula omitted] in solids by the stray-field method: prospects for imaging using Long Echo-Train Summation

We have observed Hahn-echoes resulting from Powles–Mansfield pulse-sequences for a variety of nitrogen containing solids which exhibit a range of 14 N electric quadrupole coupling constants ( C q) from 0 to 4.9 MHz. Long echo-decays were frequently obtained which allowed the collection of many echoes in one echo-train, so that the method of Long Echo-Train Summation (LETS), could be used to accumulate signal. A one-dimensional STRAFI-profile is shown for solid ammonium nitrate. The spatial resolution is discussed as a function of C q.

14N NMR single-crystal study of hexamethylenetetramine

The 14N NMR spectrum of hexamethylenetetramine (HMT) is dominated by the very large electric quadrupole coupling constant of 4.412 MHz at room temperature. Nonetheless, by carefully accounting for this interaction one can subtract its first- and second-order effects on the spectrum, leaving the much smaller anisotropic chemical shift interaction. The chemical shielding anisotropy of HMT is −8.3±3.2 ppm, small but different from zero, with an isotropic chemical shift in good agreement with the value in aqueous solution. This study illustrates how even very tiny chemical shift tensors can be extracted from the NMR spectra of quadrupolar nuclei using appropriate techniques. Copyright © 1999 John Wiley & Sons, Ltd.

Electromagnetic moments of short lived β emitters 21 F, 23 Mg, 27 Si and 39 Ca

The β-NMR spectra of 21F, 23Mg, 27Si and 39Ca which were produced in heavy ion collisions and implanted in various crystals have been observed. The magnetic moments of 21F and 27Si were determined to be |μ(21F)| = 3.9194 ± 0.0012 μN and |μ(27Si)| = 0.8653 ± 0.0003 μN, respectively. The electric quadrupole coupling constants were determined for the first time to be |eqQ(21F in MgF2)/h|= 9.94 ± 0.09 MHz, |eqQ(23Mg in MgF2)/h|= 1.96 ± 0.06 MHz, |eqQ(27Si in Al2O3)/h|= 1.90 ± 0.12 MHz, |eqQ(39Ca in CaCO3)/h|= 0.60 ± 0.04 MHz. From the present eqQ/h, the Q moments were deduced as |Q(21F)|= 110 ± 22 mb, |Q(23Mg)|= 114 ± 3 mb, |Q(27Si)|= 60 ± 13 mb and |Q(39Ca)|= 36± 7 mb. The present data were compared with the theoretical values obtained by the OXBASH shell model code.

Laboratory Measurement of theJ= 1–0 Transition of Copper Hydride

The J = 1-0 transitions of 63CuH and 65CuH were measured in the 468 GHz region with a source modulation submillimeter-wave spectrometer. The CuH molecule was generated by sputtering from copper powder in a DC glow discharge through hydrogen gas. The observed rotational transitions show the line broadening caused by the hyperfine structure due to the copper nucleus (I = 3/2). The central transition frequency, the nuclear electric quadrupole coupling constant, and the nuclear magnetic spin-rotation coupling constant were determined for each isotopomer by line-shape simulation.

Measurement of hyperfine coupling constants in the3dt2Djlevels ofK39,K40, andK41by polarization quantum-beat spectroscopy

Hyperfine quantum-beat spectroscopy has been utilized in a pump-probe configuration to measure magnetic dipole (A) and electric quadrupole (B) coupling constants in the 3d${\mathrm{}}^{2}$${\mathrm{D}}_{3\mathrm{/}2}$ and 3d${\mathrm{}}^{2}$${\mathrm{D}}_{5\mathrm{/}2}$ levels of three isotopes of potassium. For many of these levels, the largest hyperfine splitting is smaller than the natural width, and so a subnatural linewidth technique is required. In the experiments, the 3d levels are excited on the 4d${\mathrm{}}^{2}$${\mathrm{S}}_{1\mathrm{/}2}$\ensuremath{\rightarrow}3d${\mathrm{}}^{2}$${\mathrm{D}}_{\mathrm{j}}$ quadrupole transition with linearly polarized light. Time evolution of the alignment components in the d levels is probed by time-delayed resonant radiation on the 3d${\mathrm{}}^{2}$${\mathrm{D}}_{\mathrm{j}}$\ensuremath{\rightarrow}9p${\mathrm{}}^{2}$${\mathrm{P}}_{\mathrm{j}}$ transitions. Comparison of the excitation rate for two orthogonal relative polarization directions of the pump and probe laser at each delay time permits derivation of a linear polarization degree. This quantity contains beats at the various hyperfine frequencies in the d levels. Fitting the experimentally obtained time dependence to theoretical expressions allows extraction of the hyperfine coupling constants. For the 3d${\mathrm{}}^{2}$${\mathrm{D}}_{3\mathrm{/}2}$ level of $^{40}\mathrm{K}$ we obtain A=0.96(4) MHz and B=0.37(8) MHz, indicating a typical precision also obtained for the other levels and isotopes.