2g States Research Articles

Relativistic effects on the kink of nuclear charge radii in lead

The kink in the nuclear charge radii of lead isotopes is studied in the relativistic mean field approximation framework, using the parameter set NL3∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^*$$\\end{document}. Within this approach, it is shown that the small component of the single-particle Dirac spinors plays an essential role in the kink formation through its effects on the single-particle central potential. This is because the structure of this potential in terms of the σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma $$\\end{document}-scalar and ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega $$\\end{document}-vector fields and the contributions of the small component to the scalar and nucleon densities have opposite signs. The impact of the spin-orbit interaction of the valence neutrons on the kink, through its effects on their wave functions, is very small for 1i states but significant for 2g states. Due to relativistic contributions, the effects on the kink of neutrons in the valence levels of a spin-orbit doublet with j=l+1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$j=l+1/2$$\\end{document} and j=l-1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$j=l-1/2$$\\end{document} are rather different from each other, even in the limit case of neglecting their spin-orbit interaction.

Effect of the local chemical environment on oxidation resistance mechanisms in AlNbTiZr refractory high entropy alloys: A first-principles study

The present study is dedicated to the effect of local chemical environment on structure and properties of oxygen adsorption on AlNbTiZr surface from first-principle investigation. The adsorption energy results illustrate that the most stable adsorption sites are those with high content Ti, mainly due to its highest t 2g states near Fermi level. The stronger O-Al than O-Ti interaction will cause outward diffusion of Al, which explains the high concentration Al in oxide layer of AlNbTiZr experimentally. More importantly, Ti atom weakens the O-Al interaction, and thereby may weaken the stability of Al-containing oxides. Consequently, it is necessary to control experimentally by different processing methods to decrease the occurrence of Ti-Ti arrangement on the surface to improve oxidation resistance of AlNbTiZr.

Energy Transfer in the 2 u (1 D 2) Ion-Pair State of I2 by Inelastic Collisions with Noble Gas Atoms.

We investigated the energy transfer in the 2u (1D2) ion-pair state of I2 by collision with noble gas atoms, Ar, Kr, and Xe, using an optical–optical double resonance/fluorescence detection technique. By analyzing the temporal profiles of the emission from the laser-excited 2u (1D2) state at various noble gas pressures, the quenching rate constants were determined to be (4.55 ± 0.42) × 10–10, (4.23 ± 0.11) × 10–10, and (6.83 ± 0.16) × 10–10 cm3 molecule–1 s–1 for quenching by Ar, Kr, and Xe, respectively. The 2g (1D2) ion-pair state, lying in the vicinity of the 2u (1D2) state, was identified as a destination state by collision with Ar and Kr. Collision with Xe provided a new reactive pathway forming the excimer XeI(B). The rate constants were determined to be = (9.61 ± 0.63) × 10–11 cm3 molecule–1 s–1 and = (4.87 ± 0.34) × 10–11 cm3 molecule–1 s–1 for the formation of the 2g (1D2) state by collision with Ar and Kr, respectively, and = (6.55 ± 0.19) × 10–11 cm3 molecule–1 s–1 for the formation of XeI(B). The collisional cross sections calculated from the quenching rate constants were considerably larger than the molecular size, owing to the harpoon mechanism.

Sequence of superconducting states in field cooled FeCr2S4

In the present article we discuss theoretically the emergence of superconductivity in field cooled FeCr2S4. The chromium electrons form a triplet t 2g states and due to antiferromagnetic exchange with the iron spins have Zeeman splitting. Applied, during preparation, magnetic field along the moment of iron ions, successively compensates the Zeeman splittings. The chromium electrons with zero Zeeman energy form Cooper pairs induced by iron magnons. In that way, we predict theoretically the existence of sequence of superconducting states in field cooled FeCr2S4. Actually there are three different superconductors prepared applying, during preparation, different magnetic fields. In these compounds superconductivity coexist with the saturated magnetism of iron ions.

Spin density in YTiO3 : II. Momentum-space representation of electron spin density supported by position-space results

Unpaired electrons in YTiO 3 ferromagnetic crystal (below 30 K) were studied by polarized neutron diffraction (PND) and incoherent x-ray magnetic Compton scattering (MCS). These experiments provide both position and momentum representations of the electrons at the origin of the magnetic behavior, mostly those in the t 2g state of Ti atoms. A two-dimensional reconstruction was conducted from experimental and theoretical directional magnetic Compton profiles to obtain the two-dimensional magnetic electron momentum density. A superposition method is proposed to examine the coherence between results for position and momentum spaces, respectively. This model-free approach allows a straightforward cross-checking of PND and MCS experiments. An isolated Ti model is proposed to emphasize the role played by O 1 in the ferromagnetic coupling between Ti and its neighboring atoms.

New observation and analysis of the ultracold Cs2 0u+ and 1g long-range states at the asymptote 6S1/2+6P1/2

Photoassociation of ultracold Cs atoms is reported in magneto-optical trap with the modulation technique. Trap loss spectroscopy of the ultracold Cs2 molecules has been obtained experimentally. Spectroscopy data are expended to the red detuned of 70cm-1 below the 6S1/2+6P1/2 dissociation limit. Several new low lying vibrational levels belongs to the 0u+ and 1g states are identified and analyzed. The long range molecular coefficients C3 for the 0u+ and 1g states are obtained, and the corresponding empirical potential curves are derived with the spectroscopy data.

Infrared radiative decay dynamics from the γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2) ion-pair states of I2 observed by a perturbation facilitated optical-optical double resonance technique.

We report the spectroscopic and temporal analyses on the amplified spontaneous emission (ASE) from the single rovibrational levels of the Ω = 1u ion-pair series, γ 1u ((3)P2), H 1u ((3)P1), and 1u ((1)D2), of I2 by using a perturbation facilitated optical-optical double resonance technique through the c (1)Πg ∼ B (3)Π(0u (+)) hyperfine mixed valence state as the intermediate state. The ASE detected in the infrared region was assigned to the parallel transitions from the Ω = 1u ion-pair states down to the nearby Ω = 1g ion-pair states. The subsequent ultraviolet (UV) fluorescence from the Ω = 1g states was also observed and the relative vibrational populations in the Ω = 1g states were derived through the Franck-Condon simulation of the intensity pattern of the vibrational progression. In the temporal profiles of the UV fluorescence, an obvious delay in the onset of the fluorescence was recognized after the excitation laser pulse. These results revealed that ASE is a dominant energy relaxation process between the Ω = 1u and 1g ion-pair states of I2. Finally, the lifetimes of the relevant ion-pair states were evaluated by temporal analyses of the UV fluorescence. The propensity was found which was the longer lifetime in the upper level of the ASE transitions tends to give intense ASE.

Non-adiabatic transitions between first tier ion-pair states of I2 induced by collisions with Ar atoms

Non-adiabatic transitions from the I2(E0g+, D0u+, β1g and D′2g) states to first tier ion-pair (IP) states induced by collisions with Ar atoms have been investigated. The stepwise laser excitation schemes have been used for selective population of close-lying vibronic states: E, vE=13, D, vD=18, β, vβ=19 and D′2g, vD′=23. Rate constants of population of the first tier ion-pair states from the optically populated rovibronic states as well as rate constants of depopulation of the states have been determined. Analysis of the mechanism of the transitions has been carried out.We find that the λlummax≈3410Å luminescence band in the case of optical population of the D and β states cannot be described assuming the collision-induced non-adiabatic transitions only. We conclude that there is an additional radiative channel for population of the states, probably, due to the formation of the ArI2(IP) van der Waals complexes.

Nature of the Insulating Ground State of the 5d Postperovskite CaIrO3.

The insulating ground state of the 5d transition metal oxide CaIrO3 has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t(2g) states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir^{4+} spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t(2g) states to open an insulating gap. These results indicate that CaIrO_{3} can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other.

New observation and combined analysis of the Cs2 0g(-), 0u(+), and 1g states at the asymptotes 6S1/2 + 6P1/2 and 6S1/2 + 6P3/2.

We report on new observations of the photoassociation spectroscopy of ultracold cesium molecules using a highly sensitive detection technique and a combined analysis with all observed electronic states. The technique is achieved by directly modulating the frequency of the trapping lasers of a magneto-optical trap. New observations of the Cs2 0g(-), 0u(+), and 1g states at the asymptotes 6S1/2 + 6P1/2 and 6S1/2 + 6P3/2 are reported. The spectral range is extended to the red detuning of 112 cm(-1) below the 6S1/2 + 6P3/2 dissociation limit. Dozens of vibrational levels of the ultracold Cs2 0g(-), 0u(+), and 1g states are observed for the first time. The available experimental binding energies of these states are analyzed simultaneously in a framework of the generalized LeRoy-Bernstein theory and the almost degenerate perturbation theory by Marinescu and Dalgarno [Phys. Rev. A: At., Mol., Opt. Phys. 52, 311 (1995)]. The unique atomic-related parameter c3 governing the dispersion forces of all the molecular states is estimated as (10.29 ± 0.05) a.u.

Optical spectroscopy of a La3Ga5SiO14:Co2+ crystal

The absorption, luminescence, and circular dichroism spectra of a cobalt-doped La3Ga5SiO14 crystal (Ca3Ga2Ge4O14 structure, sp. gr. P321) have been studied in the range 8–300 K. The Co2+ ion has been shown to occupy the 3f tetrahedral site. For T 220 K, the 2E(2G) state is completely quenched, and only luminescence from the 4T1(4P) level is observed.

Gutzwiller electronic structure calculations applied to transition metals: Kinetic energy gain with ferromagnetic order in bcc Fe

The Gutzwiller projector technique has long been known as a method to include correlations in electronic structure calculations. We describe a model implementation for a Gutzwiller + LDA calculation in a localized-orbital restricted basis framework, emphasizing the protocol step by step and illustrating our specific procedure for this and future applications. We demonstrate the method with a classic problem, the ferromagnetism of bulk bcc Fe, whose nature is attracting fresh interest. In the conventional Stoner-Wohlfarth model, and in spin-polarized LDA calculations, the ferromagnetic ordering of iron sets in so that the electrons can reduce their mutual Coulomb repulsion, at the cost of some increase of electron kinetic energy. This balance may, however, be altered by correlations, which are strong for localized d orbitals. The present localized basis Gutzwiller + LDA calculation demonstrates how the ferromagnetic ordering of Fe may, in fact, entrain a decrease of kinetic energy at the cost of some increase of potential energy. This happens because, as foreshadowed long ago by Goodenough and others and more recently supported by LDA-DMFT calculations, correlations cause e(g) and t(2g) d orbitals to behave differently, with the weakly propagating e(g) states fully spin polarized and almost localized, and only t(2g) states forming a broad partly filled itinerant band. Owing to an intra-atomic Hund's rule exchange that aligns e(g) and t(2g) spins, the propagation of itinerant t(2g) holes is favored when different atomic spins are ferromagnetically aligned. This suggests a strong analogy with double exchange in iron ferromagnetism.

Mixed dimensionality of confined conducting electrons in the surface region of SrTiO3.

Using angle-resolved photoemission spectroscopy, we show that the recently discovered surface state on SrTiO(3) consists of nondegenerate t(2g) states with different dimensional characters. While the d(xy) bands have quasi-2D dispersions with weak k(z) dependence, the lifted d(xz)/d(yz) bands show 3D dispersions that differ significantly from bulk expectations and signal that electrons associated with those orbitals permeate the near-surface region. Like their more 2D counterparts, the size and character of the d(xz)/d(yz) Fermi surface components are essentially the same for different sample preparations. Irradiating SrTiO(3) in ultrahigh vacuum is one method observed so far to induce the "universal" surface metallic state. We reveal that during this process, changes in the oxygen valence band spectral weight that coincide with the emergence of surface conductivity are disproportionate to any change in the total intensity of the O 1s core level spectrum. This signifies that the formation of the metallic surface goes beyond a straightforward chemical doping scenario and occurs in conjunction with profound changes in the initial states and/or spatial distribution of near-E(F) electrons in the surface region.

Hyperfine structure of weakly bound levels in the lowest 1g state of molecular 87Rb2

Hyperfine structure of weakly bound levels in the lowest 1g state of molecular 87Rb2

Hyperfine structure of weakly bound levels in the lowest 1g state of molecular 87Rb2

Hyperfine structure of weakly bound levels in the lowest 1g state of molecular 87Rb2

Experimental and First‐Principles Characterization of Functionalized Magnetic Nanoparticles

Magnetic iron oxide nanoparticles synthesized by coprecipitation and thermal decomposition yield largely monodisperse size distributions. The diameters of the coprecipitated particles measured by X-ray diffraction and transmission electron microscopy are between approximately 9 and 15 nm, whereas the diameters of thermally decomposed particles are in the range of 8 to 10 nm. Coprecipitated particles are indexed as magnetite-rich and thermally decomposed particles as maghemite-rich; however, both methods produce a mixture of magnetite and maghemite. Fourier transform IR spectra reveal that the nanoparticles are coated with at least two layers of oleic acid (OA) surfactant. The inner layer is postulated to be chemically adsorbed on the nanoparticle surface whereas the rest of the OA is physically adsorbed, as indicated by carboxyl O-H stretching modes above 3400 cm(-1). Differential thermal analysis (DTA) results indicate a double-stepped weight loss process, the lower-temperature step of which is assigned to condensation due to physically adsorbed or low-energy bonded OA moieties. Density functional calculations of Fe-O clusters, the inverse spinel cell, and isolated OA, as well as OA in bidentate linkage with ferrous and ferric atoms, suggest that the higher-temperature DTA stage could be further broken down into two regions: one in which condensation is due ferrous/ferrous- and/or ferrous/ferric-OA and the other due to condensation from ferrous/ferric- and ferric/ferric-OA complexes. The latter appear to form bonds with the OA carbonyl group of energy up to fivefold that of the bond formed by the ferrous/ferrous pairs. Molecular orbital populations indicate that such increased stability of the ferric/ferric pair is due to the contribution of the low-lying Fe(3+) t(2g) states into four bonding orbitals between -0.623 and -0.410 a.u.

Association between promoters polymorphisms of matrix metalloproteinases and risk of digestive cancers: a meta-analysis

A variety of studies have been performed to elucidate the polymorphisms in promoter regions of matrix metalloproteinases (MMPs) associated with the risk of digestive cancers, and yet, results remain conflicting and heterogeneous. Thus, we undertook a systematic meta-analysis to determine the genetic susceptibility of MMPs to digestive cancers. A computerized literature search was conducted in databases of PubMed, Embase, and ISI Web of Knowledge till October 2012 for any MMP genetic association study in oral squamous, gastric, esophageal, and colorectal carcinomas. Odds ratios (OR) and 95% confidence interval (CI) were estimated for each gene under dominant and recessive models, and the heterogeneity between studies was assessed using Q test and I (2) value. Overall and subgroup analysis according to anatomical sites and ethnicity was carried out. Statistical analysis was performed with Review Manager 5.0. A total of 40 eligible publications with 68 comparisons were included in this study. For MMP1 nt-1607, individuals with 2G state could increase risk of digestive cancers in total analysis (dominant: OR=1.31, 95% CI=1.16-1.48, P<0.00001; recessive: OR=1.29, 95% CI=1.11-1.50, P=0.0009). In the subgroup of tumor sites, significant associations were also observed in esophageal cancer and colorectal cancer under both genetic models. For MMP2 nt-1306, CT or TT carriers performed significant protection against digestive cancer in the dominant model (OR=0.69, 95% CI=0.55-0.85, P=0.0007) of the overall. In the subgroup analysis, significant association was found in esophageal cancer, with borderline effects in gastric cancer and oral squamous cell carcinoma. For MMP7 -181 A/G, significant association was observed under two genetic models in the overall (dominant: OR=1.26, 95% CI=1.10-1.43, P=0.0009; recessive: OR=1.33, 95% CI=1.11-1.60, P=0.002) and in the individual cancer subgroup of esophageal cancer and gastric cancer. For MMP9 -1,562 C/T, a borderline effect was found with digestive cancers in the total and stratified analysis of the colorectal cancer under dominant model. No association was observed in either the overall or subgroup analysis for MMP3 -1,171 5A/6A. Our meta-analysis demonstrated the fact that polymorphisms in promoter regions of MMP genes might be related to the susceptibility of digestive cancers, with cancer development for MMP1 and MMP7, and a protection against cancer for MMP2 and MMP9. Further evidences with adequate sample sizes need to be conducted.

Oxygen-Vacancy-Induced Orbital Reconstruction of Ti Ions at the Interface ofLaAlO3/SrTiO3Heterostructures: A Resonant Soft-X-Ray Scattering Study

Resonant soft-x-ray scattering measurements have been performed to investigate interface electronic structures of (LaAlO(3)/SrTiO(3)) superlattices. Resonant scattering intensities at superlattice reflections show clear evidence of degeneracy lifting in t(2g) states of interface Ti ions. Polarization dependence of intensities indicates the energy of d(xy) states is lower by ~1 eV than two other t(2g) states. The energy splitting is insensitive to epitaxial strain. The orbital reconstruction is induced by oxygen vacancies and confined to the interface within two unit cells, indicating charge compensation at the polar interfaces.

Pseudo Jahn–Teller Origin of Nonplanarity and Rectangular-Ring Structure of Tetrafluorocyclobutadiene

It is shown that the pseudo Jahn-Teller effect (PJTE) in combination with ab initio calculations explains the origin of instability of the planar configuration of tetrafluorocyclobutadiene, C(4)F(4), with respect to a puckered structure and square-to-rectangle distortion of the carbon ring, and rationalizes its difference from the planar-rectangular geometry of C(4)H(4) and nonplanar (puckered) structure of Si(4)H(4). The two types of instability and distortion of the high-symmetry D(4h) configuration in these systems emerge from the PJT coupling of the ground B(2g) state with the excited A(1g) term producing instability along the b(2g) coordinate (elongation of the carbon or silicon square ring), and with the excited E(g) term resulting in e(g) (puckering) distortion. A rhombic distortion b(1g) of the ring is also possible due to the coupling between excited A(1g) and B(1g) terms. For C(4)F(4), ab initio calculations of the energy profiles allowed us to evaluate the PJTE constants and to show that the two instabilities, square-to-tetragonal b(2g) and puckering e(g) coexist, thus explaining the origin of the observed geometry of this system in the ground state. The preferred cis-trans (e(g) type) puckering in C(4)F(4) versus trans-trans puckering (b(2u) distortion) in Si(4)H(4) follows from the differences in the energy gaps to their excited electronic E(g) and A(1u) terms causing different PJTE in these two cases.

High Sensitivity Measurement and Accurate Analysis of the Vibrational Spectroscopy Near the (6S1/2+6P3/2) Dissociation limit for 1g State of Cs2

The photoassociation spectroscopic data of the long-range molecular 1g state of Cs 2 in the asymptotic range red detuned [-5.02, -2.45 cm -1 ] to the (6S 1/2 +6P 3/2 ) dissociation limit detected using photon counting technique are presented and 18 new high-lying vibrational energy levels are obtained. Fitting experimental data to the improved LeRoy–Bernstein (LRB) formula, we have obtained the long-range molecular coefficient c 3 with a high precision and also demonstrated the necessity of the improved LRB formula for more precise c 3 coefficient by analyzing the residual from fitting procedure.