Showing papers on "Quadrupole published in 1981"

Interaction site models for carbon dioxide

Abstract: The adequacy of simple potential models to describe the properties of carbon dioxide in its different phases is explored. The molecules are assumed to interact through two or three Lennard-Jones n-6 centres and a point quadrupole moment placed at the molecular centre of mass. Good agreement with a wide range of properties is obtained for a three-centre model with n=12 and a value of the quadrupole moment which is somewhat smaller than the experimental one.

Polarization transfer in elastic electron scattering from nucleons and deuterons

Abstract: We present a description, including relevant formulas and numerical estimates, of a set of polarization transfer experiments which appear to offer a feasible way to separate the deuteron charge and quadrupole form factors and measure the neutron and proton electric form factors. The experiments require a 2 to 4 GeV high-intensity, high-duty factor, longitudinally polarized electron beam and require that the polarization of the recoiling hadron be measured in a second, analyzing, scattering. The relevant asymmetries are fairly large, and our calculations show that they are sensitive to different models obtained from existing data. Attention is called to the fact that the proposed deuteron measurements will require new 10% measurements of vector and tensor analyzing powers of deuterons with kinetic energy from 150 to 450 MeV.

Improved computational procedure for evaluation of overlapping hyperfine parameter distributions in Mossbauer spectra

Abstract: An improved method for computer analysis of Mossbauer spectra in terms of hyperfine parameter distributions is presented. The method evaluated by Phillips and Twomey (1962) is extended to include an additional constraint on the endpoints of the distribution function, and this algorithm is combined with an iteration procedure. This application of the method is illustrated in fitting a spectrum with a distribution in magnetic hyperfine fields using the iteration procedure to obtain directly from the spectrum values for the isomer shift, quadrupole interaction and line area ratios. The method is also used to determine the Fe2+/Fe3+ ratio from a paramagnetic spectrum with broadened non-Lorentzian lines. To obtain this an average correlation between isomer shift and quadrupole splitting has been assumed for iron in each of the two valence states. It is shown that spectra originating from symmetric distribution functions can be fitted equally well assuming either of two different correlations between isomer shift and quadrupole splitting, and an equation relating these two correlations is derived.

Giant resonances in nuclei

Abstract: A review is given of the present situation of electric giant resonances in nuclei. Starting with the properties of the well-known electric dipole resonances the authors summarise the known experimental facts on resonances with other angular momenta and parities. They mainly discuss the giant quadrupole and giant monopole resonances which are known best. The difficulties connected with the extraction of nuclear structure information from the experimental cross sections are discussed in detail. They also review the theoretical developments in this field and emphasise especially microscopic models and the corresponding results. As far as possible the experimental facts are compared with the theoretical results.

Chemical shielding tensor and 13C–14N dipolar splitting in single crystals of L‐alanine

Abstract: Chemical shielding tensors have been determined for three chemically distinct carbons in a single crystal of L‐alanine using proton‐enhanced 13C NMR. The results indicate that the most shielded direction is perpendicular to the sp2 plane for the carboxyl carbon and the C3 axis for the methyl carbon. 13C–14N dipolar splittings have been observed for the Ca carbon, causing further complication in spectral analysis. Since the 14N quadrupole coupling constant is of comparable order with the 14N Zeeman interaction, 14N quadrupole interaction is effective in the 13C–14N dipolar splittings. The 14N quadrupole effect is observed and demonstrated by calculation and the sign of the quadrupole coupling constant e2Qq has been determined to be positive. The chemical shielding tensor for the Ca carbon is determined by considering the 13C–14N dipolar interaction and the 14N quadrupole interaction. It is shown that the 14N quadrupole interaction causes the asymmetric doublet pattern in the 13C NMR signal for the Ca carbo...

On the anisotropy of the cosmological background matter and radiation distribution. I - The radiation anisotropy in a spatially flat universe

Abstract: The expected anisotropy in the microwave background radiation on both large and small angular scales has been calculated. Primordial adiabatic and isothermal fluctuations are considered for a variety of initial power-law fluctuation spectra Vertical Bard/sub m/(k)Vertical Bar/sup 2/proportionalk/sup n/ in a spatially flat universe. The calculated temperature anisotropy on small angular scales is below the current observational upper limits if W> or approx. =1. An appreciable dipole and smaller quadrupole anisotropy are also produced. These are generated by fluctuations in the mean gravitational potential associated with small-amplitude large-wavelength fluctuations in the matter distribution on scales > or approx. =10--100 Mpc. Most of the observed dipole anisotropy could be attributed to this effect, as could the possible detection of a quadrupole anisotropy. More generally, the large-scale radiation anisotropy measurements constrain the index of the initial fluctuation spectrum: n> or approx. =0 for isothermal fluctuatons, and n> or approx. =3 for adiabatic fluctuations. A further implication is that, in general, our peculiar velocity relative to distance shells of matter only coincides with that measured relative to the background radiation (inferred from the dipole moment) at a redshift z> or approx. =0.1. At small redshifts there can be significant deviations in both directionmore » and amplitude.« less

The generator coordinate method applied to variational perturbation theory. Multipole polarizabilities, spectral sums, and dispersion coefficients for helium

Abstract: It is shown that a suitable variant of the generator coordinate method can be used for accurate variational perturbation theory calculations. The test problems chosen are calculations of the dipole, quadrupole, and octupole polarizabilities, spectral sums, two‐body dispersion coefficients, and nonadditive three‐body dispersion coefficients for the ground state of atomic helium. An accurate explicitly correlated wave function for the unperturbed problem is utilized along with explicitly correlated basis functions for the pseudospectra. The dipole results are in excellent agreement with previous high accuracy calculations. The quadrupole and octupole results are expected to be the most accurate ones currently available. Estimates of some hexadecapole properties are made.

Rotational spectrum, structure, and intramolecular force field of the ArClCN van der Waals complex

Abstract: The rotational spectrum of the ArClCN van der Waals complex has been assigned using pulsed Fourier transform microwave spectroscopy in a Fabry‐Perot cavity with a pulsed supersonic nozzle as the molecular source. ArClCN is T‐shaped and the data were fit to the Watson rotational parameters and an exact expression for the Cl and N nuclear quadrupole coupling. The spectroscopic constants for Ar35ClCN are A′′ = 6152.5411(21) MHz, B′′ = 1577.0362(8) MHz, C′′ = 1246.7514(6) MHz, τ1 = −576.0(2) kHz, τ2 = −97.28(8) kHz, τaaaa = −234.8(17) kHz, τbbbb = −55.97(10) kHz, τcccc = −21.60(7) kHz, χClaa = 37.9468(23) MHz, χClbb = −79.5239(20) MHz, χNaa = 1.6403(22) MHz, and χNbb = −3.4571(20) MHz. The centrifugal distortion constants are used to derive the intramolecular force field and a normal coordinate analysis is performed. The Cl nuclear quadrupole coupling tensor indicates that the field gradients in ClCN are slightly perturbed upon complex formation but not enough to proscribe their use in structural determinatio...

Molecular beam electric resonance spectroscopy of the nitric oxide dimer

Abstract: Microwave and radiofrequency spectra have been observed for (NO)2 using the technique of molecular beam electric resonance spectroscopy. Precise values have been determined for rotational, nuclear quadrupole coupling and spin-rotation constants of the ground electronic state treated as a singlet state. The values obtained are A = 25829·4803(20) MHz, B = 5614·3093(4) MHz, C = 4605·4396(12) MHz xaa = -4·0652(2) MHz, xbb - xcc = -8·5498(6) MHz caa = 10·4(5) kHz, cbb = 13·8(4) kHz, ccc = 0·8(4) kHz. The electric dipole moment has also been determined: μ = 0·17120(2) D. From these data (NO)2 is interpreted to have a symmetric cis-planar structure with the structural parameters r NN = 2·33(12) A, r NO = 1·15(1) A, ∠NNO = 95(5), 1/2(r NN + r NO) = 2·444(8) A. The quadrupole coupling constants of the nitrogen nuclei and the dipole moment demonstrate that little electron rearrangement occurs on dimer formation. In addition xaa and xbb - xcc indicate that the unpaired π electrons lie in the plane of the dimer imply...

The quadrupole moments of carbon dioxide and carbon disulphide

Abstract: The electric quadrupole moments of carbon dioxide and carbon disulphide have been measured through the birefringence induced in gaseous samples over a range of temperature. The value for CO2, Θ = (-14·98 ± 0·50) × 10-40 C m2, is consistent with earlier measurements, showing that the temperature-independent hyperpolarizability contribution to the birefringence is insignificant. For CS2, Θ = (+12·0 ± 0·6) × 10-40 C m2. The positive sign reflects the increased importance of the π electron contribution to Θ in CS2.

Fast atom bombardment quadrupole mass spectrometry

Abstract: Fast atom bombardment quadrupole mass spectrometry (F.A.B.Q.M.S.) is shown to have considerable benefit for the production of structural mass spectral data from non-volatile organic compounds.

Molecular structure of ArDF: An analysis of the bending mode in the rare gas–hydrogen halides

Abstract: The rotational spectrum of the ArDF van der Waals molecule has been assigned using pulsed Fourier transform microwave spectroscopy in a Fabry‐Perot cavity with a pulsed supersonic nozzle as the molecular source. The DF nuclear spin–nuclear spin and D nuclear quadrupole coupling constants are 12.5(11) and 194.7(20) kHz, respectively. These constants yield equivalent structural information and are used together with the rotational constant to obtain the structure of ArDF. The rotational spectrum of ArHF was also re‐examined and the HF spin–spin constant found to be 49.0(19) kHz. The structure of ArHF was then obtained from the rotational and HF spin–spin constants. Finally, the vibrationally averaged angles in 14 complexes of the type X–H(D)Y (X=Ar, Kr, or Xe; Y=F, Cl, or Br) are calculated using a multipole potential and compared with experiment. The agreement between the observed and calculated angles is very good.

Sum rules for inhomogeneous Coulomb systems

Abstract: Using the stationary equilibrium BBGKY hierarchy and some weak spatial decay properties of the correlations, we derive exact sum rules for the equilibrium distribution functions of ionic systems. Our results apply to both homogeneous and nonuniform systems. They show that when there is decay in such systems, then the total excess charge in the vicinity of a given number of fixed ions is zero, and that this excess charge has no dipole nor quadrupole moment. The implications for the static structure factor and for the dielectric tensor are discussed.

Algebraic approach to nuclear quasi-molecular spectra

Abstract: It is suggested that nuclear quasimolecular spectra are dominated by dipole rather than quadrupole degrees of freedom. An algebraic approach to these dipole modes in terms of the group U(4) is proposed. One of the dynamical symmetries of the corresponding algebraic structure, O(4), is discussed and shown to yield spectra of molecular rotation-vibration type.

Dipole and Quadrupole Anisotropy of the 2.7 K Radiation

Abstract: Results of measurements of the dipole and quadrupole anisotropy of the microwave background radiation are reported. Balloon-borne measurements of the temperature difference between two horn antennas pointed 90 deg apart and 45 deg from the zenith were carried out at frequencies of 24.8, 31.4 and 46.0 GHz to determine three dipole and four quadrupole parameters. When combined with data from two previous balloon flights, a dipole anisotropy of 3.78 + or - 0.30 mK in the direction 11.6 + or - 0.2 h RA, -12 + or - 5 deg dec is obtained. The measurements reveal a spectral index of 0.04 + or - 0.28 between 19.0 and 46.0 GHz, indicating that the dipole effect arises from an intrinsic anisotropy in the temperature of the background and/or a first-order Doppler shift due to solar motions. A statistically significant quadrupole effect is also detected which is attributed to the intrinsic anisotropy of the 2.7 K background.

Optical second-harmonic generation in atomic vapors with focused beams

Abstract: Processes leading to second-harmonic generation when a single polarized beam is focused into neutral or partially ionized atomic vapor are considered, including electric-field-induced third-order mixing, and quadrupole and magnetic dipole processes. Estimates of the relative strengths of these processes are given. In addition, the polarization properties given by the tensor susceptibilities are discussed in detail.

The Microwave Spectrum of Imidazole; Complete Structure and the Electron Distribution from Nuclear Quadrupole Coupling Tensors and Dipole Moment Orientation

Abstract: Spectra have been measured for eleven isotopic forms of imidazole, including single substitutions at each nucleus in turn. A complete rs-structure is obtained. The ring structure is: N(1)-C(2) = 1.364 Å, C(2)-N(3) = 1.314 Å, N(3)-C(4) = 1.382 Å, C(4)-C(5) = 1.364 Å, C(5)-N(1) = 1.377 Å, ≮N(1)C(2)N(3) = 112.0°, ≮C(2)N(3)C(4) = 104.9°, ≮N(3)C(4)C(5) = 110.7°, ≮C(4)C(5)N(1) = 105.5° and ≮C(5)N(1)C(2) = 106.9°. The N(1)-H(1) distance is 0.998 Å, while the C-H distances are all very close to 1.078 Å. The bonds N(1)-H(1) and C(2)-H(2) lie close to the external bisectors of the respective ring angles, but C(4)-H(4) and C(5)-H(5) are each displaced by several degrees from these bisectors towards N(3) and N(1) respectively. The electric dipole moment is established as 3.67 (5) D from Stark effects, directed almost parallel with the line joining the nitrogen nuclei. The properties and orientations of the two 14N-nuclear quadrupole tensors have been investigated, in particular through the spectra of the two mono-14N-imidazoles.

A measurement of the hyperfine structure of C17O

Abstract: It is pointed out that the isotope of carbon monoxide, CO-17, has appreciable hyperfine structure caused by the electric quadrupole and the magnetic dipole interactions of the O-17 nucleus which has a spin of 5/3. During a radioastronomical study of the structure and dynamics of cold interstellar clouds, it was found that the Bok globule B335 had an extremely small velocity dispersion such that the hyperfine components are clearly resolved. A graph is provided which shows the antenna temperature (a measure of intensity) of the CO-17 emission as a function of frequency. The hyperfine constants and line frequencies were redetermined for the CO-17 J=1 yields 0 rational transition. The observation of CO-17 was carried out with a 7 meter Cassegrain antenna during 1979 and 1980. The CO-17 molecular line parameters are listed in a table.

A continuum theory for quadrupole relaxation of ions in solution

Abstract: A simple continuum theory for quadrupole relaxation rates of ions in polar solvents is presented. The predicted rates agree fairly well with experimental rates determined for various ions in several solvents. The surprising success of the relatively crude continuum model is discussed and the implications for molecular theories of quadrupole relaxation are indicated.

Basis set error in quadrupole moment calculations

Abstract: For a series of first row diatomic molecules, quadrupole moments obtained from restricted Hartree-Fock level calculations with various basis sets are compared with exact values obtained from numerical solution of the Hartree-Fock equations. Significant basis set errors are frequently observed, even with large and/or exponent optimized basis sets. Estimates of the correlation errors in the quadrupole moments lead to the conclusion that basis set error is probably just as serious as correlation error for most molecular quadrupole moment calculations.

Theory of fluids of non-axial quadrupolar molecules

Abstract: Thermodynamic perturbation theory is used to derive expressions for thermodynamic quantities for a fluid composed of non-axial quadrupolar molecules. These expressions have the same form as the corresponding ones for axial molecules, but with the single axial dipole and quadrupole moments (μ, Q) replaced by effective moments which are rotationally invariant combinations of the components of the multipole moments μ and Q. If the quadrupole moment is weak, so that the perturbation expansion can be terminated at the second order term, a single effective axial quadrupole moment used in the axial expressions correctly reproduces the free energy and pressure second virial coefficient. For stronger quadrupole moments, where third and higher order terms are needed, this ‘effective axial’ approximation is generally poor, and one must use the correct non-axial expressions. For pure ethylene it is shown that the effective axial approximation gives accurate results for the third order free energy term A 3, and hence ...

Identification of electric quadrupole O2 and N2 lines in the infrared atmospheric absorption spectrum due to the vibration-rotation fundamentals

Abstract: Analysis of long path atmospheric absorption spectra and of laboratory absorption spectra in the 1600 cm−1 region has resulted in the identification of atmospheric quadrupole lines of O2 in its fundmental vibrational band within the electronic ground state. This led to the identification of similar atmospheric quadrupole lines of N2 in the 2400 cm−1 region.

Dynamic deuterium NMR in liquid crystalline solvents: Ring inversion of cyclohexane‐d12

Abstract: The application of deuterium NMR spectroscopy of molecules dissolved in liquid crystalline solvents to study intramolecular dynamic processes is demonstrated using the ring inversion kinetics of cyclohexane‐d12. The spectra of C6D12 dissolved in phase V and in hexyloxyazoxybenzene were studied over the temperature range −36 to +115 °C, and were found to exhibit a very pronounced line shape variation with temperature. At low temperatures (<−10 °C) the spectrum consists of two symmetric doublets due to the axial and equatorial sites. The doublet splittings are due to the quadrupole interactions of the corresponding deuterons. Upon increasing the temperature the lines broaden until finally the spectrum transforms into a single doublet with a spacing corresponding to the mean quadrupole splitting of the axial and equatorial deuterons. In an Appendix the line shape theory for two interacting nuclei of spin I = 1 which undergo mutual exchange is presented, and this theory is used to quantitatively interpret the...