Large Quadrupole Moment Research Articles

Proton skin of 8B in a microscopic model

The experimentally predicted existence of a proton skin in 8B is confirmed by dynamical microscopic cluster model calculations. The thickness of the proton skin in 8B is 0.5 fm while in 8Li a 0.4 fm thick neutron skin has been found. It is shown that the large quadrupole moment of 8B partly comes from the very distortable 7Be core.

Pressure shifts and electron scattering lengths in atomic and molecular gases

Photoabsorption or photoionization spectra of CH3I are discussed as a function of perturber pressure for 11 different binary gas mixtures consisting of CH3I and each one of 11 different gaseous perturbers. Five of the perturbers were rare gases and six were nondipolar molecules. The energy shifts of CH3I Rydberg states become independent of n, the principal quantum number, for n≥10. The energy shifts for n≥10 vary in a linear fashion with perturber number density. The electron scattering lengths for the perturbers are extracted from the shifts using Fermi theory in which the polarization term is that of Alekseev and Sobel’man. These scattering lengths are compared with those from swarm and time-of-flight experiments. It is found that the uncorrected shift scattering lengths correspond to the zero energy or near-zero energy scattering lengths obtained from extrapolated swarm and time-of-flight data. It is found that plots of scattering length vs polarizability α (ᾱ for molecules) define two linearities, one for the rare gases and one for molecules, CO2 being an exception to the latter linearity (presumably because of its large quadrupole moment). For a given polarizability, it is also found that molecules exhibit a larger scattering length than the rare gases. These results are discussed and consequences for scattering cross sections are elaborated.

The chemical nature of nitrogen in native soil organic matter

H. Knicker, R. Frtind and H.-D. Ltidemann Institut for Biophysik und physikalische Biochemie der Universit~it, W-8400 Regensburg, FRG Fossil fuels and soil organic matter (SOM) together contain approximately five times more carbon than the biota and the atmosphere. Of this, soil organic matter accounts for about 30 % of the carbon present. In addition, SOM has an average carbon/nitrogen ratio of 10/1 and contains a huge fraction of the total ni- trogen available for plant growth [1]. Taking into account that the abundance of nitrogen in the earth's crust is much lower than that of carbon, this is a signif- icant fraction of the total nitrogen acces- sible to the biosphere. Under natural soil conditions, without the addition of miner- al fertilizers, SOM provides the majority of the nitrogen necessary for plant growth. It is also thought to be respon- sible for the interaction between agricul- tural biocides and the soil [5-7]. The chemical structure of this ubiquitous material, SOM, and especially the chem- ical nature of the nitrogen are thus of great and general importance. The mo- lecular structure of the nitrogen- containing fraction is, however, still a matter of controversy [2-4]. Structural models based on partial chem- ical analysis claim that a significant part of the nitrogen is present in the form of heteroaromatic structures, while NMR- spectroscopic studies on lSN-enriched composts and recent humic material found approximately 85 % of the signal intensity in the amide/peptide region of chemical shift and no signals in the range typical for heteroaromatic nitrogen. A major fraction of the native soil organic matter has been in the soil for several hundred to several thousand years [8, 9]. Compared to these time spans, laboratory-produced material has been fermented for at most 1 year, and it could be argued that heteroaromatic structures are only produced after much longer fermentation periods. This criti- cism may be overcome by the study of lsN-CPMAS spectra of soil organic mat- ter with natural lSN levels. This has not been achieved hitherto, because the low natural abundance (0.4 %) and the small gyromagnetic ratio of the 15N nucleus and therefore its low sensitivity in NMR experiments appeared to make this experiment an impossible one. The most abundant 14N-isotope (99.6 %) cannot be studied by high-resolution NMR because its large nuclear quadrupole moment leads to very broad and unresolved signals, especially in solid-state NMR [101. In previous systematic studies on 15N- enriched composts and organic soil extracts [11] our group optimized all spectral parameters for the ~sN-CPMAS experiment. A crude estimate showed that it should be possible to obtain 15N spectra with a tolerable signal-to-noise ratio after the accumulation of approximately one million transients. In the present paper we report on the first successful results of such experiments. Six German soils were studied as detailed in Table 1. In Figs. 1 and 2 some of the spectra obtained are shown. They fully corrobo- rate the conclusions drawn from the stud- ies of short-term composting exper-

The hyperfine muon-nucleus interaction andP-odd effects in the one-photon 2s ? 1s transition of light muonic atoms

The weak interaction of neutral currents of the negative muon and a nucleus results inP-odd correlations in the one-photon 2s → 1s transition of light muonic atoms. If the standard electroweak model is used, the weak mixing of hyperfine components of the μ-atom 2s and 2p 1/2 orbits makes the main contribution to these correlations. A new mechanism of acting the hyperfine structure on theP-odd correlations is considered in the present work. The fact is that the hyperfine muon-nucleus interaction mixes the 2p 1/2 and 2p 3/2 orbits effectively in light muonic atoms whose nuclei have large quadrupole moments. As a result, two new sublevels arise for each of two valuesF±=(I ± 1/2) of the total angular μ-atom momentum (I is the nuclear spin). The contributions of these sublevels to theP-odd correlations can be comparable with each other. The most strikes manifestation of the given effect occurs for berillium and boron, where the 2s and 2p 3/2 orbits may have close energies. Taking the above effect into account can lead to considerable modification of results against earlier calculations. In particular, theP-odd correlations can vanish and change sign. They can be additionally increased by a factor of several tens.

Radiation detected resonance ionization spectroscopy on208Tl and242fAm

An ultra-sensitive laser spectroscopic method has been developed for the hyperfine spectroscopy of short-lived isotopes far off stability produced by heavy ion induced nuclear reactions at very weak intensity (> 1/s). It is based on resonance ionization spectroscopy in a buffer gas cell with radiation detection of the ionization process (RADRIS). As a first on-line application of RADRIS optical spectroscopy at242fAm fission isomers is in progress at the low target production rate of 10/s. The resonance ionization has been performed in two steps utilizing an excimer dye laser combination with a repetition rate of 300 Hz. The first resonant step proceeds through terms which correspond to wavelengths of 466.28, 468.17 or 426.56 nm; the second non-resonant step is achieved with the 351 nm radiation of the excimer laser itself, running with XeF. The frequency scans of the tuneable dye laser at 466.28 and 468.17 nm exhibit broad resonance ionization signals, the latter with a large isotope shift between242fAm and243Am which is in accordance with the large quadrupole moment of the242fAm fission isomer.

NQR and Neutron Diffraction in Scheelites

Abstract Measurements of the spin-lattice relaxation time for rhenium in KReO4 and NH4ReO4 are reported; relaxation rates are extremely fast due to the large quadrupole moment of Re. Calculations of the electric field gradient in KReO4 show that the EFG is a very sensitive function of the orientation of the anion in the unit cell as well as of the unit cell dimensions, and that geometrical effects make a major contribution to the temperature dependence. Neutron diffraction in these two salts has been employed to determine the temperature dependence of structural parameters over a wide range of temperature, and preliminary results are reported.

Breitlinien 185Re- und 187Re-Festkörper-NMR-Spektroskopie an Metaperrhenaten mit alkylsubstituierten Kationen der V. Hauptgruppe / Wideline 185Re and 187Re Solid-State NMR Spectroscopy of Metaperrhenates with Alkyl-Substituted Cations of Main Group V

127I solid-state NMR spectra of metaperiodates with alkyl- or aryl-substituted cations of main group V yield second order quadrupole effects due to the distortion of the tetrahedra surrounding the iodine nuclei. In some cases the 127I quadrupole effects were found to become very small or even vanish. Thus the isomorphous metaperrhenates should also be accessible by 185Re, 187Re solid-state NMR. Owing to the very large quadrupole moments of the 185Re and 187Re isotopes, very small distortions or changes in dynamical effects can be detected in systems with such voluminous cations. The solid-state NMR spectra of (CH3)4AsReO4 yield the calculated 185Re, 187Re second order quadrupole effects. These result from two kinds of differently distorted ReO4- tetrahedra. X-ray investigations and calculations based on a point charge model for (CH3)4SbReO4 manifest the inaccessibility of quadrupole effects by wideline solid-state NMR in a magnetic field of Bo = 4.698 Tesla.

Foreign-gas pressure broadening and shift of ammonia transition lines in the ν 2 vibrational bands

Foreign-gas broadening and shift have been measured for transitions in the ν 2, 2ν 2 and ν 4 bands of ammonia using a diode laser spectrophotometer. The measurements were performed by using foreign-gases such as CO 2, N 2, air, H 2, and He at room temperature. The pressure-broadening and shift coefficients may be useful in modelling planetary atmospheres and the recently developed infrared (i.r.) ammonia laser. The experimental results are compared with the Anderson-Tsao-Curnutte theory for broadening CO 2 and N 2, which have large quadrupole moments. The agreement is satisfactory on the average.

127I, 185Re and 187Re Solid State NMR Measurements on (CH3)4AsIO4 and (CH3)4AsReO4

Tetramethylarsonium-metaperiodate shows 127I solid state NMR signals without any visible quadrupole splitting. Due to the very large nuclear quadrupole moments of the rhenium isotopes 185,187Re, the analogous Re compound exhibits the expected second order quadrupole NMR effects. The measured 185,187ReRe NMR powder spectra contain superimposed signals arising from two different types of ReO- 4 tetrahedra, indicating that part of the ReO4 - anions deviate only slightly from tetrahedral symmetry, while the other part are nearly undistorted ReO4 - anions. The temperature dependence of the solid state NMR spectra reveals phase transitions for both compounds, which are confirmed also by DSC analyses. Furtherm ore, the DSC analysis of the Re compound again proves the existence of the two different types of ReO4 - tetrahedra in the lattice of the high temperature modification.

Possible test at Jupiter of the nonsymmetric gravitational theory.

Radiometric data generated during spacecraft flybys of Jupiter have the capability to provide an interesting constraint on the coupling of cosmions in the nonsymmetric gravitational theory (NGT) of Moffat. It is shown that the close flyby of Jupiter by Pioneer 11 could imply a possible limit on the NGT $l$ parameter of the Sun of ${l}_{\ensuremath{\bigodot}}<2800$ km, a limit which could affect the ability of the NGT to account for the precession of the perihelion of Mercury with a large solar quadrupole moment.

The first high resolution direct NMR observation of an f-block element

The last decade has seen a dramatic increase in the importance of the organometallic chemistry of the lanthanide elements. In particular, iodides, cyclopentadienyls, and bis(trimethylsilyl)amides of Sm(II), Eu(II), or Yb(II), due to their unique reactivity (e.g., as selective reducing agents), have attracted much attention. Yet high resolution, solution-state NMR, one of the organometallic chemists most informative tools, has not previously been applied to the direct observation of an f-block element, excluding complexes of the f{sup 0} La(III). The reason for this neglect is probably because the majority of complexes (except those of La(III), Yb(II), and Lu(III)) are paramagnetic, and many of the NMR-active f-block nuclei have large quadrupole moments. Yet for certain of these elements spin-{1/2} isotopes exist, and the range of diamagnetic compounds is rapidly increasing. As a case in point, {sup 171}Yb is a spin-{1/2}nucleus, with a natural abundance of 14.27% and a moderately sized, positive gyromagnetic ratio (4.4712 {times} 10{sup 7} rad T{sup {minus}1} s{sup {minus}1}); these features combine to give a receptivity four times greater than that of {sup 13}C. Three solid-state, wide-line studies of this nucleus have appeared. The authors now report {sup 171}Yb chemical shift solution NMR data for the series of Yb(II) complexes.

Quadrupole collective properties of 114Cd

The nucleus 114Cd has been Coulomb excited using beams of 16O, 40Ca, 58Ni and 208Pb. Several new states have been observed and an almost complete set of reduced E2 matrix elements for the lowest-lying positive-parity states in 114Cd have been measured. In total, about 40 E2 matrix elements have been determined in a model-independent way, including the static quadrupole moments of the 4 + 1, 6 + 1, 2 + 2 and 2 + 3 states. Large negative static quadrupole moments were found for the 4 + 1 and 6 + 1 states and a large positive quadrupole moment for the 2 + 2 state. All E2 matrix elements involved in the deexcitation of the quintuplet of states at an energy of about 1.2 Me V were determined. The data are compared with predictions by various models, including a configuration mixing calculation within the framework of the IBA model, the harmonic vibrator and a model in which the states of a near-harmonic vibrator are mixed with those of a rotational intruder band with a large deformation. Although no perfect match is obtained, the data favour a vibration-like structure involving levels up to the four-quadrupole phonon multiplet.

The magnetic field of Uranus

A spherical harmonic model of the planetary magnetic field of Uranus is obtained from the Voyager 2 encounter observations using generalized inverse techniques which allow partial solutions to complex (underdetermined) problems. The Goddard Space Flight Center “Q3” model is characterized by a large dipole tilt (58.6°) relative to the rotation axis, a dipole moment of 0.228 G RU³, and an unusually large quadrupole moment. Characteristics of this complex model magnetic field are illustrated using contour maps of the field on the planet's surface and discussed in the context of possible dynamo generation in the relatively poorly conducting “ice” mantle.

Low-temperature reactions of some atomic ions with molecules of large quadrupole moment: C 6F 6 and c-C 6H 12

Reactions of He +,C + and N + ions with C 6F 6, and c-C 6H 6 were examined at 27, 68 and 297 K using both CRESU and SIFT techniques. Within the experimental uncertainties, all of the rate coefficients are found to be temperature-independent in this range. The results are discussed in relation to the most recent theoretical models describing the influence of the quadrupole moment on the temperature dependence of ion-molecule reaction rate coefficients.

ChemInform Abstract: Microwave Spectrum of Methyliodosilane: Determination of the Dipole Moment and eqQ of an Asymmetric Top Molecule Containing an Atom with a Large Nuclear Quadrupole Moment.

Abstract Microwave spectra of methyliodosilane and its deuterated species have been measured. A least-squares analysis for the observed frequencies yielded rotational constants and quadrupole coupling constants of the parent species as: A = 14 747.837 ± 0.054, B = 1893.504 ± 0.003, C = 1728.518 ± 0.003, χ aa = −1012.65 ± 0.43, η a χ aa = χ bb − χ cc = −161.96 ± 0.37, and | χ ab | = 478.29 ± 0.84 (all in MHz). The dipole moment of the parent species was determined from Stark effect measurement of some hyperfine components of the 3 03 -2 02 transition to be μ l = 1.862 ± 0.005, μ a = 1.831 ± 0.005, and μ b = 0.336 ± 0.005 D. Also the product among μ a , μ b , and χ ab was concluded to have a positive sign from the Stark shift observed. A brief discussion has been given on the procedure for determining the dipole moment of a molecule containing an atom with a large nuclear quadrupole coupling moment.

Mean-lifetime measurements within the superdeformed second minimum in 132Ce.

A rotational band has been studied in $^{132}\mathrm{Ce}$ to a spin above 50\ensuremath{\Elzxh}. Lifetime measurements have resulted in a large quadrupole moment corresponding to a deformation \ensuremath{\beta}\ensuremath{\sim}0.5. This is consistent with the moment of inertia determined from the energy-level spacing. These data are the first measurements of collectivity of discrete lines at high spin within the superdeformed second minimum.

185Re and 187Re solid‐state NMR of metaperrhenates

Abstract127I solid‐state NMR investigations of specific metaperiodates with alkyl‐ or aryl‐substituted cations of main Group V revealed second‐order quadrupole effects, except in the case of tetraethylammonium and tetramethylphosphonium metaperiodate. In these compounds the 127I quadrupole interactions are either very small or vanish. This allowed the approximate evaluation of the electric field gradients of the analogous isomorphous metaperrhenates. Despite the very large nuclear quadrupole moments of the rhenium isotopes, the estimated values of the 185Re and 187Re quadrupole coupling constants of tetraethylammonium and tetramethylphosphonium metaperrhenate have an order of magnitude accessible to solid‐state NMR measurements. The 185Re and 187Re NMR powder spectra of rhenium compounds in non‐cubic lattice structures were measured for the first time. The complete 185Re and 187Re solid‐state NMR spectra of polycrystalline tetramethylphosphonium metaperrhenate were observed, showing temperature‐dependent second‐order quadrupole splittings. In this compound the ReO anions show very small deviations from tetrahedral symmetry, which were estimated from a point charge model and the measured quadrupole splittings. In contrast, the tetrahedral symmetry of the ReO ions of tetraethylammonium metaperrhenate is nearly undistorted, because no quadrupole splittings of the 185Re and 187Re signals were detectable in the powder NMR spectrum.

The quadrupole moment of cyanogen: a comparative study of collision-induced absorption in gaseous C2N2, CO2, and mixtures with argon

The collision-induced spectra of C2N2 gas and a gaseous mixture of C2N2 and Ar at 298 K have been obtained in the spectral region below 120 cm−1 using far-infrared laser and microwave techniques as well as a Fourier-transform spectrometer. In addition, the collision-induced spectra of a gaseous mixture of CO2 and Ar are reported at temperatures of 233 and 298 K in the spectral region below 230 cm−1. The theoretical values for the spectral moments α1 and γ1 for CO2 are much smaller than the experimental values, as expected for a molecule with a relatively large quadrupole moment. However, for CO2–Ar mixtures, the agreement between the theoretically and experimentally determined spectral moments is relatively good, resulting in a value of 4.6 B for the quadrupole moment of CO2 instead of the generally accepted value of 4.3 B. The quadrupole moment of C2N2 is estimated to be 6.2 ± 0.4 B from our data and the theory for the spectral moments, if a correction is made for an overestimate of the quadrupole moment similar to that obtained for the CO2–Ar mixture. This value is considerably smaller than a previously reported calculated result of 9.0 B. Line-shape expressions based on information theory (IT6) do not yield good agreement with experiment, a result that is attributed to the large anisotropy of the molecules.

Microwave spectrum of methyliodosilane: Determination of the dipole moment and eqQ of an asymmetric top molecule containing an atom with a large nuclear quadrupole moment

Microwave spectra of methyliodosilane and its deuterated species have been measured. A least-squares analysis for the observed frequencies yielded rotational constants and quadrupole coupling constants of the parent species as: A = 14 747.837 ± 0.054, B = 1893.504 ± 0.003, C = 1728.518 ± 0.003, χ aa = −1012.65 ± 0.43, η a χ aa = χ bb − χ cc = −161.96 ± 0.37, and | χ ab | = 478.29 ± 0.84 (all in MHz). The dipole moment of the parent species was determined from Stark effect measurement of some hyperfine components of the 3 03-2 02 transition to be μ l = 1.862 ± 0.005, μ a = 1.831 ± 0.005, and μ b = 0.336 ± 0.005 D. Also the product among μ a , μ b , and χ ab was concluded to have a positive sign from the Stark shift observed. A brief discussion has been given on the procedure for determining the dipole moment of a molecule containing an atom with a large nuclear quadrupole coupling moment.

Stability and structure of cluster ions in the gas phase: Carbon dioxide with Cl−, H3O+, HCO+2, and HCO+

Thermodynamic values for the clustering reactions of carbon dioxide with Cl−, H3O+, HCO+2 , and HCO+ were measured with a pulsed electron-beam high-pressure mass spectrometer. The measured enthalpy changes are reproduced satisfactorily by the ab initio molecular orbital calculations. While Cl−(CO2)n is of the symmetric geometry, H3O+(CO2)n, HCO+2(CO2)n, and HCO+(CO2)n are of the form of the shell plus surroundings. The small fall-off of the bonding energy for the cluster growth is ascribed to the large quadrupole moment of CO2 as well as those on the shell.