Electronic Asymmetry Research Articles

Constraints on four-Fermi contact interactions from low-energy electroweak experiments

We investigate the constraints on four-Fermi contact interactions from low-energy lepton-quark and lepton-lepton scattering experiments --- polarization asymmetries in electron (muon)-nucleon scattering experiments, cesium and thallium atom parity violation measurements, neutrino-nuclei and neutrino-electron scattering experiments. These constraints are then combined by assuming the lepton and quark universalities and SU(2)*U(1) gauge invariance of the contact interaction, which leave independent six lepton-quark and three pure-leptonic interactions.Impacts of these constraints on models with an additional Z-boson are briefly discussed. We also present updates of the low-energy constraints on the S and T parameters.

DiracR-Matrix Modeling of Spin-Induced Asymmetry in the Scattering of Polarized Electrons from Polarized Cesium Atoms

Recent experiments by Baum, Raith, and co-workers to measure the spin-induced asymmetries in electron scattering from cesium have stimulated theoretical work to interpret these measurements. We present Dirac $R$-matrix calculations of the interference asymmetry function, and of the spin-orbit and spin-exchange asymmetries, for comparison with experimental data at 7 and 13.5 eV and with nonrelativistic predictions of the spin-exchange asymmetry from the convergent close coupling method. We find that a simple relativistic target model provides a basis for the understanding and analysis of ongoing experiments.

A combined polarized target/ionization chamber for measuring the spin dependence of nuclear muon capture in laser polarized muonic 3He

We describe a device used in experiment 1231 at LAMPF and in e683 at TRIUMF to study the spin dependence of the reaction μ − + 3He → 3H + v μ . In order to study the spin dependence, we needed to form and polarize muonic 3He and in the same volume detect the 1.9 MeV tritons created in the reaction. Furthermore, the recoil direction of the tritons had to be determined. The apparatus served both as a polarized target and as a detector. The detector, a gridded ion chamber, was incorporated inside a 51 polarized target that was filled with 8 atm of 3He and 100 Torr of N 2 and rubidium metal. At the operating temperature of the device (205–230°C) the rubidium number density was approximately 10 15 atoms/cm 3. Muons that stopped in the target formed muonic helium atoms, which were then polarized by collisions with optically pumped Rb vapor. Two high-powered GaAlAs diode laser arrays were used to polarize the Rb in the 100 cm 3 fiducial volume located inside the ion chamber. The ion chamber produced clean signals from the reaction tritons despite having to operate under the extreme conditions required for efficient optical pumping. The direction of the tritons was determined by analyzing the shapes of the ionization pulses. The muon polarization was measured using the decay electron asymmetry.

Electronic Asymmetry: Theoretical Background, Ligand Design, and Applications

A brief review with 10 refs. featuring an extended HMO and structure-correlation study of the edge-bridged tetrahedron, the design of electronically asym. bidentate ligands, and applications in an Fe-based storage device.

Measurement of the Proton's Neutral Weak Magnetic Form Factor

We report the first measurement of the parity-violating asymmetry in elastic electron scattering from the proton. The asymmetry depends on the neutral weak magnetic form factor of the proton which contains new information on the contribution of strange quark-antiquark pairs to the magnetic moment of the proton. We obtain the value $G_M^Z= 0.34 \pm 0.09 \pm 0.04 \pm 0.05$ n.m. at $Q^2=0.1$ (GeV/c)${}^2$.

ChemInform Abstract: Role of Electronic Asymmetry in the Design of New Ligands: The Asymmetric Hydrocyanation Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Virtual Compton scattering off protons at moderately large momentum transfer

The amplitudes for virtual Compton scattering off protons are calculated within the framework of the diquark model in which protons are viewed as being built up by quarks and diquarks. The latter objects are treated as quasi-elementary constituents of the proton. Virtual Compton scattering, electroproduction of photons and the Bethe-Heitler contamination are discussed for various kinematical situations. We particularly emphasize the r\^ole of the electron asymmetry for measuring the relative phases between the virtual Compton and the Bethe-Heitler amplitudes. It is also shown that the model is able to describe very well the experimental data for real Compton scattering off protons.

Influence of Electronic Asymmetry on the Spectroscopic and Photodynamic Properties of the Primary Electron Donor in the Photosynthetic Reaction Center

Resonance Raman and subpicosecond resolution transient absorption data are presented on the reaction center (RC) from the Rb. sphaeroides (M)H202L/(L)L131H double mutant. This RC contains a bacteriochlorophyll/bacteriopheophytin heterodimer primary electron donor (D), as a result of introducing a Leu at M subunit residue 202, as well as a hydrogen bond to the ring-V keto group of the BChl component, as a result of introducing a His at L subunit residue 131. The double mutant shows a longer lifetime (∼40 ps) for the lowest excited singlet state and a lower quantum yield of charge separation (∼25%) than observed previously for the heterodimer single mutants (M)H202L and (L)H173L. These changes are ascribed in large measure to a decrease in the contribution of the accessory pigment BChlL to the initial stage of charge separation. This perturbation in turn results from an upshift in the free energy of D+BChlL- relative to P+BChlL- (where P is the homodimer primary donor of wild-type RCs). This shift is due to the substantially elevated oxidation potential of the heterodimer in the (M)H202L/(L)L131H double mutant (ca. +765 meV) relative to that of the homodimer in wild-type RCs (ca. +500 meV). Both the rate of internal conversion of the excited primary donor and the characteristics of the near-infrared ground state absorption of the dimer appear to be intermediate between those found for the (M)H202L single mutant and wild-type RCs. Resonance Raman profiles obtained via excitation at several wavelengths across the heterodimer absorption band suggest that there is a change in the nature and perhaps ordering of the two lowest excited states of the heterodimer in the double mutant compared with the single mutant. Collectively, these data indicate that the addition of a hydrogen bond to the more easily oxidized (and less easily reduced) BChl component decreases the inherent electronic asymmetry of the heterodimer and partially restores characteristics of the wild-type homodimer.

Acetylenyl-Linked, Porphyrin-Bridged, Donor−Acceptor Molecules: A Theoretical Analysis of the Molecular First Hyperpolarizability in Highly Conjugated Push−Pull Chromophore Structures

We describe the theoretical basis for the exceptionally large molecular first hyperpolarizabilities inherent to (5,15-diethynylporphinato)metal-bridged donor−acceptor (D−A) molecules. β values relevant for hyper-Rayleigh experiments are calculated at 1.064 and 0.830 μm for a complex with such a structure, [5-((4‘-(dimethylamino)phenyl)ethynyl)-15-((4‘‘-nitrophenyl)ethynyl)-10,20-diphenylporphinato]zinc(II), and are 472 × 10-30 and 8152 × 10-30 cm5/esu, respectively. The values are 1 order of magnitude larger than that calculated for any other porphyrin bridged donor−acceptor chromophore studied to date. The considerably enhanced hyperpolarizability arises from the significant excited-state electronic asymmetry manifest in such structures (derived from the strong bridge-mediated D−A coupling enabled by the largely porphyrin-based excited state) and the large bridge-centered oscillator strength in this new class of D−bridge−A molecules. Our analysis of NLO properties (based upon INDO/SCI calculations within the sum over states formalism) shows a sensitivity to the degree of cumulenic character in the ground state. Calculations on structurally related multiporphyrin systems suggest candidate chromophores with further enhanced optical nonlinearities.

Role of Electronic Asymmetry in the Design of New Ligands: The Asymmetric Hydrocyanation Reaction

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTRole of Electronic Asymmetry in the Design of New Ligands: The Asymmetric Hydrocyanation ReactionT. V. RajanBabu and Albert L. CasalnuovoView Author Information Department of Chemistry, The Ohio State University 100 West 18th Avenue, Columbus, Ohio 43210 Central Research and Development Experimental Station, The DuPont Company Wilmington, Delaware 19880 Cite this: J. Am. Chem. Soc. 1996, 118, 26, 6325–6326Publication Date (Web):July 3, 1996Publication History Received20 March 1996Published online3 July 1996Published inissue 1 January 1996https://doi.org/10.1021/ja9609112Copyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1428Altmetric-Citations122LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (113 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Chemical reactions,Ligands,Phosphorus,Selectivity,Stereoselectivity Get e-Alerts

Crystal and molecular structure of ?-(dimethylsilanediyl)dimethylene-bis(trimethylsilylmethyl)molybdio-tris(trimethylphosphine)molybdenum(I)(4 Mo-Mo)

Single crystal structure determination of the title compound shows that the molecule contains a Mo-Mo quadruple bond [4Mo-Mo = 2.164(1) A] between two atoms differing in both formal oxidation state (+ 1 and + 3) and coordination number (4 and 3). This combination of electronic and stereochemical asymmetry makes the compound quite unique within the general class of metalmetal multiply bonded species.

Measurable parameters of neutron decay

The effect of the general vector, axialvector, scalar and tensor interactions on the theoretical description of neutron decay is investigated. Results of least squares adjustment computations for the weak coupling constants are presented (neutron decay and several nuclear beta decay observables have been employed). A simple calculation method, which makes it possible to get analytical formulae for many important distributions and quantities of neutron decay, is described. The sensitivities of the electron and proton spectra and asymmetries and of two combined electron-proton asymmetries to the determination of the most important phenomenological parameters are studied by statistical methods.

Photoisomerization of Asymmetric Indobenzimidazolo Cyanine Dyes

AbstractThe isomerization kinetics of three indobenzimidazolo polymethine cyanines have been investigated and compared with the corresponding properties of the parent symmetric dyes. A significant alternation of the π bond orders in the polymethine chain was found in the ground states (S0) of the asymmetric dyes. A similarly alternant behaviour was exhibited by the calculated S0 potential energy barriers for twisting around the polymethine chain bonds of the asymmetric carbocyanine, whereas uniform barriers were found for the symmetric parent compounds. The experimentally observed sequence of back‐isomerization activation energies was interpreted on the basis of these theoretical results. It was suggested by some spectral and kinetic fluorescence properties, and it was confirmed by the calculated polymethine‐chain π bond orders of the lowest singlet excited states (S1) that the electronic asymmetry induced by the different terminal heterocycles was strongly reduced upon excitation of these dyes to their S1 states. In spite of this, the trans‐cis photoisomerization of asymmetric cyanines occurred invariably around those bonds having the highest π bond orders in the ground state. A tentative theoretical explanation of this systematic behaviour is reported.

Quantum mechanical electronic width and shift of spectral lines over the full line profile—Electronic asymmetry

The electronic contributions to the asymmetry of spectral lines are investigated by considering frequency-dependent electronic widths and shifts. The asymmetry due to the frequency-dependent electronic width leads to increased blue line wings. The asymmetry of the line profile resulting from the shifts depends on the energy difference between the considered energy level and perturbing ones. For hydrogen lines the red wings are shifted to the red side whereas the blue wings are shifted to the blue side.

Photon angular correlations and pressure-dependent effects of helium 21P and 31P excitation by electrons

The orientation and alignment parameters of the 21P and 31P excited states of helium at an incident electron energy of 81.6 eV have been remeasured for electron scattering angles from 25 degrees to 5 degrees and extended down to 2 degrees . The studies investigate a wide range of experimental conditions and measurement techniques, including beam alignment, electron and photon angular distribution asymmetries in both the singles and coincidence detection modes, in order to establish better precision in the measurements. Nevertheless the present coherence lambda , chi and gamma a, parameters for He(21P) and He(31P) state excitation for scattering angles in the range theta e=2 degrees to 25 degrees are collectively not in good agreement with any single distorted wave, first Born or close coupling model predictions, although there are ranges of scattering angles where the individual measured parameters are in good agreement with a particular theory. Radiation trapping effects on the 31P state lifetime enabled the relative relaxation rates for the population, orientation and alignment, i.e. rank 0, 1 and 2 multipoles, of the excited state to be measured. The effects of these relaxation rates on the measured intensities and the coherence parameters are quantified. The lifetime, which can be measured an order of magnitude more quickly than the state parameters, reflects these relaxation rates and provides a reliable guide to radiation trapping effects. Radiation trapping influences the state parameters down to the lowest background operating pressure of 10-7 Torr at which the measurements have been made.

Asymmetry and Energy Spectrum of Electrons in Bound-Muon Decay

Theoretical values for the muon decay rate and the emitted electron energy spectrum and several kinds of asymmetry parameters for the angular distribution of the electrons in bound-muon decay are given in numerical tables and figures for 16O, 27Al, 28Si, 40Ca, 56Fe, 90Zr, 96Mo, 118Sn, 208Pb, and 209Bi. The present results are based on the general formalism of the angular distribution of emitted electrons in bound-muon decay published in Prog. Theor. Phys. 78, 114 (1987), in terms of the multipole series of the relativistic electron wave functions. The effect of finite nuclear size on the wave functions is properly taken into account for both the bound muon and the emitted electron.

On the baryon, lepton-flavour and right-handed electron asymmetries of the universe

Non-perturbative electroweak effects, in thermal equilibrium in the early universe, have the potential to erase the baryon asymmetry of the universe, unless it is encoded in a B - L asymmetry, or in some “accidentally” conserved quantity. We first consider the possibility that the BAU may be regenerated from lepton flavour asymmetries even when initially B - L = 0. We show that provided some, but not all the lepton flavours are violated by ΔL ≠ 0 interactions in equilibrium, the BAU may be regenerated without lepton mass effects. We next examine the possibility of encoding the baryon asymmetry in a primordial asymmetry for the right-handed electron, which due to its weak Yukawa interaction only comes into chemical equilibrium as the sphalerons are falling out of equilibrium. This would also raise the possibility of preserving an initial baryon asymmetry when B - L = 0.

Nuclear tests for the strange charge from factor of the nucleon

It is shown that the measurements of elastic and inelastic scattering of neutrinos and parity-violating asymmetry of longitudinally polarized electrons on spin-isospin zero nuclei would yield model independent information about the strangeness charge form factor. Nunerical estimates of the contribution of this form factor are presented for 4He, 12C and 16O nuclei in impulse approximation using strangeness vector from factors of the nucleon recently suggested in the literature. A general relation between the P-odd asymmetry in electron scattering and the cross sections of neutrino and unpolarized electron scattering on spin zero nuclei is obtained.

Constitution and fluorescence spectra of unsymmetrical polymethine dyes

The regularities in the fluorescence spectra of typical electron-unsymmetrical polymethine dyes were found to be similar to those of the corresponding symmetrical dyes, in contrast to absorption spectra. The fluorescence spectra exhibit constant vinylene shifts (c. 100 nm) for a widely varied degree of electronic asymmetry, band maxima almost free of deviations, and band shapes characteristic of most organic dyes which are slightly affected by the nature of a solvent. In contrast, in the absorption spectra, increase in electronic asymmetry is accompanied by decreasing vinylene shifts, increasing deviations, notably changing band shapes and increasing solvatochromic effects. Based on quantum-chemical calculations, the atomic charges and bond orders of unsymmetrical dyes were shown to be considerably more equalized in the excited than in the ground state, which causes the essential difference between their fluorescence and absorption spectra.

Influence of the electronic asymmetry in NH (1Δ) state Λ doublets on the photodissociation dynamics of HN3 and DN3

The influence of the electronic asymmetry in the 1Δ(A′) and 1Δ(A″) Λ doublets of NR (R=H,D) on the photodissociation dynamics of hydrazoic acid (RN3) has been investigated. Hydrazoic acid was prepared in its first excited electronic state, Ã1A″. A variety of scalar (internal state and translational energy distribution) and vectorial (angular distribution, rotational alignment, correlation between translational and rotational motion) properties of the ejected NH or ND fragment were analyzed by Λ-doublet-specific Doppler profile measurements. While the population of the 1Δ(A′) and 1Δ(A″) states are equal, the vector correlations for both Λ sublevels are different. NR(A″) products are preferentially ejected in the original plane formed by the parent, and the recoil of NR fragments in the symmetric Δ(A′) state is preferentially perpendicular to that plane. The vector correlation between the translational and the rotational motion of the fragment also indicates a strong nonplanar dissociation geometry for NR products in the Δ(A′) state. About 50% of the ND(A′) product rotation is generated by a torsional motion, while 80% of the ND(A″) fragments are formed with J being aligned perpendicular to the recoil direction (MJ=0).