Showing papers on "Quadrupole published in 1986"

Forbidden Lines in ns2npk Ground Configurations and nsnp Excited Configurations of Beryllium through Molybdenum Atoms and Ions

Abstract: Observed and predicted wavelengths of magnetic dipole lines arising within ground configurations of the type ns2npk(n=2 and 3, k=1 to 5) are compiled. For n=2 the compilation includes the elements B through Kr, and for k=5 it extends to Mo. For n=3 Al through Mo are included. In addition the 2s2p excited configuration of the Be i isoelectronic sequence for Be through Kr and 3s3p of the Mg sequence for Mg through Mo are included. For each line we give a calculated value for the transition probability obtained mainly from the Dirac‐Fock method or from the use of scaled radial integrals. The calculated wavelengths are obtained from known energy levels or from levels derived from scaled radial integrals. A small group of electric quadrupole lines seen in astronomical sources are included. The list contains 1660 predicted wavelengths in the range 100 A to 25.9 mm and 406 observed wavelengths in the range 325 A to 609 μm.

Acoustic multipole sources in fluid-filled boreholes

Abstract: Acoustic well logging methods historically have been based on the excitation and reception of axisymmetric wave phenomena in a fluid-filled wellbore. We consider the reception of nonsymmetric wave phenomena excited by acoustic multipole sources. The first three orders of multipoles are the monopole, dipole, and quadrupole, and we examine these particular sources in detail. Existing sonic tools make use of a monopole source, while more recently, both dipole and quadrupole sources have been explored. An exact frequency-wavenumber domain representation of the acoustic field in the borehole due to a multipole source is formulated and numerical methods are used to compute synthetic space-time domain waveforms. We consider wideband monopole, dipole, and quadrupole excitations with center frequencies of 1, 4, and 12 kHz, and treat both slow and fast formation models. Finally, we derive low-frequency, far-field asymptotic expressions for the monopole, dipole, and quadrupole waveforms. At frequencies such that the shear wavelength is on the order of the borehole diameter or less, the difference between the monopole, dipole, and quadrupole waveforms is primarily in the nature of the surface wave mode which they excite: the monopole excites a Stoneley, or tube mode; the dipole excites a flexural mode; and the quadrupole excites a screw mode. By comparison, the compressional and shear head waves and the trapped waveguide modes do not change as much as the order of the multipole is changed.At low frequencies, where the shear wavelength is much longer than the diameter of the hole, the monopole excites a dominating tube mode, while the dipole and quadrupole excites dominating shear waves. Low-frequency asymptotic expressions for the waveforms agree well with the numerically computed waveforms.

Pulsar timing and general relativity

Abstract: Techniques are described for accounting for relativistic effects in the analysis of pulsar signals. Design features of instrumentation used to achieve millisecond accuracy in the signal measurements are discussed. The accuracy of the data permits modeling the pulsar physical characteristics from the natural glitches in the emissions. Relativistic corrections are defined for adjusting for differences between the pulsar motion in its spacetime coordinate system relative to the terrestrial coordinate system, the earth's motion, and the gravitational potentials of solar system bodies. Modifications of the model to allow for a binary pulsar system are outlined, including treatment of the system as a point mass. Finally, a quadrupole model is presented for gravitational radiation and techniques are defined for using pulsars in the search for gravitational waves.

A General, Gauge Invariant Analysis of the Cosmic Microwave Anisotropy

Abstract: A general, gauge-invariant analysis of the large-scale anisotropies in the cosmic background radiation produced by arbitrary scalar, vector, or tensor perturbations in open, closed, or flat Robertson-Walker spacetimes (with no cosmological constant) is presented. The multipole moment predictions for the scale invariant spectrum and Omega = 1 universe predicted by inflationary cosmologies are contrasted with those for other spectra and for open and closed universes. Using the measured value of the dipole moment, limits are set on the expected value of the quadrupole moment as a function of Omega for various spectra.

Doppler effects due to thermal macromotion of ions in an rf quadrupole trap

Abstract: The second-order Doppler shift is an important source of systematic error in rf quadrupole trapped ion frequency standards. This shift can be reduced by cooling the secular motion of the ion cloud with a light background gas at low pressure. Using a thermalized ion cloud model, it is possible to relate the Doppler shift to the temperature of the ion cloud. It is shown that, in practice, the measured frequency of the first-order Doppler sidebands can be used to determine the ion cloud temperature.

The microwave spectrum of the K=0 states of Ar–NH3

Abstract: The microwave spectrum of Ar–NH3 has been obtained using molecular beam electric resonance spectroscopy and pulsed nozzle Fourier transform microwave spectroscopy. The spectrum is complicated by nonrigidity and most of the transitions are not yet assigned. A ΔJ=1, K=0 progression is assigned, however, and from it the following spectroscopic constants are obtained for Ar–14NH3: (B+C)/2=2876.849(2) MHz, DJ =0.0887(2) MHz, eqQaa =0.350(8) MHz, and μa =0.2803(3) D. For Ar–15NH3 we obtain (B+C)/2 =2768.701(1) MHz and DJ =0.0822(1) MHz. The distance between the Ar atom and the 14NH3 center of mass RCM is calculated in the free internal rotor limit and obtained as 3.8358 A. In the pseudodiatomic approximation, the weak bond stretching force constant is 0.0084 mdyn/A which corresponds to a weak bond stretching frequency of 35 cm−1. The NH3 orientation in the complex is discussed primarily on the basis of the measured dipole moment projection and the quadrupole coupling constant. It is concluded that the Ar–NH3 in...

Gamma decay of isovector giant resonances built on highly excited states in 111Sn.

Abstract: Gamma-ray transition-energy spectra up to E/sub ..gamma../approx. =33 MeV have been measured for the decay of the compound nucleus /sup 111/Sn( populated at excitation energies up to E(approx. =100 MeV. Above E/sub ..gamma../approx. =20 MeV an excess of gamma rays over the contribution from the isovector giant dipole resonance is observed in the energy range where the isovector giant quadrupole resonance built on excited states is expected. The width of the giant dipole resonance in /sup 108,111/Sn( shows a large increase with increasing nuclear temperature and angular momentum.

Finite-field many-body perturbation theory. X. Electric field gradients and other properties of N2

Abstract: Finite-field MBPT calculations have been carried out for the electric field gradient and other electric properties of the nitrogen molecule. On the basis of correlation corrections computed through the fourth order in the electron correlation perturbation the infinite order MBPT result for the electric field gradient at the nitrogen nucleus has been estimated. The corresponding result combined with the NQR coupling constant for N 2 leads to the 14 N nuclear quadrupole moment of 0.0205 ± 0.0010 barn in agreement with the experimental atomic measurement and other molecular calculations. The MBPT estimate of the quadrupole moment of N 2 gives −1.107 ± 0.038 au in agreement with the most recent experimental value.

Ratio of electric quadrupole to magnetic dipole amplitudes in the nucleon-delta transition

Abstract: We have analyzed available data on magnetic dipole and electric quadrupole amplitudes for the photoproduction of pions around the delta region, in the framework of a phenomenological ..gamma..N..delta.. interaction and background. The unitarity constraint via Watson's theorem limits severely the range of allowed gauge couplings in the ..gamma..N..delta.. vertex. We obtain (-1.5 +- 0.2)% as the ratio of the electric quadrupole to magnetic dipole resonant amplitudes, a value of the same order of magnitude as predicted in the skyrmion model of baryons. This ratio suggests a deformed structure of the nucleon and the delta isobar.

Finite-field many-body perturbation theory. IX: Electric properties of ammonia

Abstract: The complete fourth-order MBPT expansion is applied to the accurate study of the multipole moments and polarizabilities of ammonia by using the finite-field perturbation method and a large partly optimized GTO/CGTO basis set. The results for the dipole and quadrupole moments and the dipole polarizability are in very good agreement with the available experimental data. The accurate theoretical data (μe = 0·5898ea 0, ϑe = -2·210ea 2 0, (α xx )e = 13·73e 2 a 2 0 E -1 h, (α zz )e = 15·66e 2 a 2 0 E -1 h, (Cxx, xx )e = 27·3e 2 a 4 0 E -1 h, (Czz, zz ) e = 30·2e 2 a 4 0 E -1 h, (Cxz, xz )e = 24·0e 2 a 4 0 E -1 h, (Cxy, xy )e = 19·7e 2 a 4 0 E -1 h) are used to evaluate the quality of the interaction surfaces for van der Waals complexes of NH3 computed with a smaller and less flexible basis set. The reasons for some discrepancies between earlier calculations of the dipole polarizability of NH3 are elucidated as well.

Magnetic-Dipole and Electric-Quadrupole Transitions in the Ground-State Configurations of the Germanium and Arsenic Isoelectronic Sequences

Abstract: Calculations of energies and transition probabilities are reported for forbidden lines in the ground configurations of the germanium (4p2) and arsenic (4p3) isoelectronic sequences up to silver (Z = 47). Configuration interaction and relativistic effects were included in the framework of the HXR and HFR self-consistent-field methods. Transition probabilities have been obtained in intermediate coupling using parameter values for the 4p2 and 4p3 configurations obtained either by fitting or by extra-(inter)polation when experimental energy levels are missing. Except for Ge I and As I, transition probabilities are reported for the first time for all these ions. A note concerning transition probabilities for Fe XII is also appended.

Nuclear quadrupole moment of nitrogen from combined fully numerical and discrete basis-set calculations on NO+ and N2

Abstract: The electric field gradients at the nuclei in NO + and N 2 are calculated by combining fully numerical and large-basis LCAO methods. The Q ( 14 N) values from the two molecules are consistently equal to 0.0205 b, as compared with the current value of 0.0193(8) b from N + 2p3p 1 P 1 .

Shielding and Antishielding of Nuclear Quadrupole Moments

Abstract: The development of the theory of shielding and antishielding of nuclear quadrupole moments is reported. The various contributions to the Sternheimer shielding and antishielding factors are discussed. Also the history of the different calculational techniques is outlined.

Spontaneous radiation of an electron beam in a free-electron laser with a quadrupole wiggler

Abstract: A calculation is presented of spontaneous radiation emitted by an electron beam passing through a continuously rotating quadrupole magnetic undulator It is shown that radiation spectrum emitted in forward direction of beam propagation has four peaks, corresponding to four betatron frequencies Utilizing the Madey theorem, a stimulated emission is calculated and presented as gain versus frequency curves, for different values of the quadrupole magnetic field A free‐electron laser operating at two or three radiation frequencies with a quadrupole magnetic wiggler is suggested

Random-phase-approximation study of the response function describing optical second-harmonic generation from a metal selvedge.

Abstract: Optical second-harmonic generation in centrosymmetric metals stems from the breaking of inversion symmetry in the selvedge and from nonlocal effects. In the present work a random-phase-approximation description of the nonlocal nonlinear conductivity tensor of an inhomogeneous jellium is given. Main emphasis is devoted to a study of the electric dipole response from the selvedge, and to the magnetic dipole and electric quadrupole responses from the profile region and the bulk. A detailed analysis of the tensor symmetry schemes associated with the p\ensuremath{\cdot}A and A\ensuremath{\cdot}A interactions is presented. Dipole and quadrupole transitions are identified, and the role of direct and indirect quantum processes is discussed. On the basis of the so-called infinite-barrier model, a few numerical results are given.

The 4f states of He2: A new spectrum of He2 in the near infrared

Abstract: A new spectrum of the He2 molecule has been discovered in the region 5100–5900 cm−1. It is identified as the 4f–3d Rydberg transition of He2 with a weak contribution of 4d–3p in the same region. The uncoupling of l from the internuclear axis in both the triplet and the singlet system is almost complete in the 4f complex; the appropriate quantum number is N+ corresponding to the rotational angular momentum of the He+2 core. The electronic fine structure in each N+ level depends on the dipole polarizability α of the core and its anisotropy as well as on the quadrupole moment Q2 and higher moments Q4,... of the core. Conversely, from the observed structure some of the quantities characterizing the core have been determined, e.g., α=1/3(2α⊥+α∥) =2.82 ±0.02, Q2=1.39±0.13, Q4=0.99±0.14, all in atomic units. The detailed rotational analysis of the spectrum shows that widespread perturbations occur in the triplet 4f levels, the largest affecting the N=6,N+=3 and N=9,N+=7 levels which are shifted towards higher en...

Experiments on size-selected metal cluster ions in a triple quadrupole arrangement

Abstract: A high flux of positively and negatively charged metal cluster ions was produced in a sputtering arrangement, energy-analyzed and mass-filtered The resulting mono-dispersed cluster ion beam was introduced into a quadrupole drift tube, where it interacted with a laser beam or reacted with an introduced gas All inelastic scattering events were recorded with a subsequent quadrupole mass filter The results exhibited a high sensitivity of positively and negatively charged silver clusters Ag n ± (n≤16) with respect to photofragmentation Ion-molecule reactions of nickel clusters with carbon monoxide allowed to synthesize very interesting organometallic and carbonyl compounds, and the maximum number of ligands provided interesting structural indications

Polarized raman optical activity and the bond polarizability model

Abstract: We show that, within a simple version of the bond polarizability model based on the approximation of axially-symmetric bonds, the polarized Raman optical activity is simply double the depolarized in a given band. Many of the bands in preliminary polarized and depolarized Raman optical activity spectra obtained with a new optical multichannel instrument accord with this result, which indicates that this and related models provide a useful starting point for interpreting ROA spectra in terms of structural detail. Additionally, our spectra imply that isotropic contributions can usually be neglected in most Raman optical activity bands, but that electric quadrupole contributions, while smaller than magnetic dipole contributions, are still usually significant.

NMR pulse response and measurement of the quadrupole coupling constant of I=3/2 nuclei

Abstract: The rf pulse response of a system of I=3/2 nuclei which experience identical first‐order quadrupole splitting is investigated using the density matrix method. A general expression is derived for the time evolution of the in‐phase magnetization following a rectangular pulse applied at the center line frequency. The maximum amplitude of the magnetization associated with the center line, and the length of pulse that gives rise to it, are calculated as a function of the ratio of the quadrupole splitting to the amplitude of the rf field. Data obtained for 23Na in a single crystal of NaNO3 are in fairly good agreement with the theoretical form. The theory has been extended to the case where the nuclei are situated at equivalent sites in a polycrystalline sample. The length of pulse that maximizes the amplitude of the FID of 23Na in a powder sample of NaNO3 has been measured as a function of the amplitude of the rf field. The quadrupole coupling constant, found by fitting the data to the theoretical form, is in ...