Electron momentum distribution in multiply-ionized neon atoms

We present momentum-space properties of multiply ionized neon atoms as a function of the degree of ionization of the atom. In particular, we have calculated the Compton profiles of all possible ionized states of neon atoms with electronic configurations 1s^m2sⁿ2p^q, m=1-2, n=0-2, q=0-6. The radial single-electron radial wave functions, obtained from the Hartree-Fock atomic model, were converted into momentum space wave functions by applying appropriate Fourier transformation. The values of the Compton profiles from the present calculation can be used to interpret experimental cross sections of variously ionized neon atoms colliding with other atoms. Compton profiles of neutral neon atoms, available in the literature, are in excellent agreement with the present calculation.     

Iron isotope effect on Tc in optimally-doped (Ba,K)Fe2As2 (Tc = 38 K) and SmFeAsO1−y (Tc = 54 K) superconductors

We report the iron isotope effect on a transition temperature (T_c) in an optimally-doped (Ba,K)Fe₂As₂ (T_c = 38 K) and SmFeAsO_1−y (T_c = 54 K) superconductors. In order to obtain the reliable isotope shift in T_c, twin samples with different iron isotope mass are synthesized in the same conditions (simultaneously) under high-pressure. We have found that (Ba,K)Fe₂As₂ shows an inverse iron isotope effect α_Fe = −0.18 ± 0.03 while SmFeAsO_1−y shows a small iron isotope effect α_Fe = −0.02 ± 0.01, where the isotope exponent α is defined by T_c ∼ M^−α (M is the isotopic mass). The results show that α_Fe changes in the iron-based superconductors depending on the system. The distinct iron isotope effects imply the exotic coupling mechanism in the iron-based superconductors.     

Changes in nuclear mean square charge radii of stable Krypton isotopes

The isotope shifts of stable even Kr isotopes (A=78 throughA=86) in the optical transitions at 432 nm and 557 nm were measured by means of polarization laser spectroscopy. The observed shifts are consistent with earlier results for other transitions. From the isotope shifts the changes in the nuclear mean square charge radiiδ〈r ²〉 were inferred using preliminary muonic isotope shift data. Starting from⁷⁸Kr, a monotonic decrease of 〈r ²〉 with increasing mass number is found throughout theg _9/2 neutron shell. The effect onδ〈r ²〉 of nuclear deformations as well as possible contributions due to changes in the skin thickness of the nuclear charge distribution are discussed.     

Lithium and antimony adsorbed on graphene studied by first-principles calculations

We have investigated the Sb and Sb₂ doping of graphene and the effect of Li_n (n = 2-4) atoms in detail. We find chemisorption only when we replace C with Sb and Sb₂ and distort the lattice. The additional adsorption of Li atoms changes the electronic band structure of the system.     

Theoretical study of conductance in stretched monatomic nanowires

Recent experiments showed that the last, single channel conductance step in monatomic gold contacts exhibits significant fluctuations as a function of stretching. From simulations of a stretched gold nanowire linked to deformable tips, we determine the distribution of the bond lengths between atoms forming the nanocontact and analyze its influence on the electronic conductance within a simplified single channel approach. We show that the inhomogeneous distribution of bond lengths can explain the occurrence and the 5% magnitude of conductance fluctuations below the quantum conductance unit g₀=2e²/h.     

Cu-isotope effect on the spin-Peierls transition of CuGeO3

The Cu-isotope effect on the spin-Peierls transition temperature T _SP in samples of the Cu²⁺ linear-chain compound CuGeO₃ has been determined by dc-magneticsusceptibility and specific-heat measurements. A downshift of the spin-Peierls transition by about 0.1 K for the ⁶⁵Cu-isotope enriched ⁶⁵CuGeO₃ as compared to ^natCuGeO₃ containing the natural mixture of isotopes is found consistently in the magnetization and specific heat. This result suggests different isotope effects on the phonon characteristic frequency θ₀ on the one hand and on the spin-phonon coupling constant g on the other hand. However, the isotope effect on T _SP is smaller than estimated if all atoms were to contribute to ω₀ and only the Cu atoms to g.     

H/D isotope effect of 1H MAS NMR spectra and 79Br NQR frequencies of piperidinium p-bromobenzoate and pyrrolidinium p-bromobenzoate

H/D isotope effects onto ⁷⁹Br NQR frequencies of piperidinium p-bromobenzoate were studied by deuterium substitution of hydrogen atoms which form two kinds of N–H?O type hydrogen bonds, and the isotope shift of ca. 100 kHz were detected for a whole observed temperature range. In addition, ¹H MAS NMR spectra measurements of piperidinium and pyrrolidinium p-bromobenzoate were carried out and little isotope changes of NMR line shape were detected. In order to reveal effects of molecular arrangements into the obtained isotope shift of NQR frequencies, single-crystal X-ray measurement of piperidinium p-bromobenzoate-d2 and density-functional-theory calculation were carried out. Our estimation showed the dihedral-angle change between piperidine and benzene ring contributes to isotope shift rather than those of N–H lengths by deuterium substitution.     

Eine Hyperfeinstruktur-Analyse der Grundkonfigurationen 5d 8 6s 2 und 5d 9 6s des Pt-I Spektrums

The hyperfine structure of the ground configurations 5d ⁸ 6s ² and 5d ⁹ 6s of the stable Platin isotopes 194, 195, 196, 198 was analyzed. For the isotope 195 a complete set of the magnetic splitting constantsA is given. TheA constants of the levels 5d ⁸ 6s ^{2 3} P ₁ and¹ D ₂ were determined for the first time. From these data the electronic splitting constants a_{6 s}=l010(10) mK, a_{d 3/2}=57 (6) and a_{d 5/2}=27 (2) mK could be evaluated. The effect of core polarization is discussed and a fieldκ _cp=?5.6(1.0) a.u. per 5d-electron spin is found. Also the isotopic shift is determined and for the mean quadratic nuclear charge radius the valueΒδ <r ²>=0.095 (10) fm² is derived.     

Inelastic collision cross section of excited molecules

The (v′=6,J′=43) level in theB ¹Π _u electronic state of Na₂ has been selectively populated by excitation with the 4 880 Å line of the argon laser. Through collisions with He atoms energy is transferred to neighbouring rotational states in Na₂ and the density of these states is determined by observing fluorescence to electronic ground state. From previous measurement of the lifetime of theB ¹Π _u state and new measurements of the intensities of collision induced spectral lines as a function of He pressure, absolute collision cross sections for all rotational transitions up to ΔJ=±5 have been obtained. The total cross section for all rotational transitions observed is σ _rot ^total =65±15 Ų. Preliminary results about collision induced vibrational transitions are also presented.     

First-principle study of structural and electronic properties of ternary layered Ta2AlC

The structural and electronic properties of ternary layered Ta₂AlC ceramics have been studied using the first-principle method based on the density-functional theory. We have obtained the equilibrium lattice parameters and the equilibrium atomic positions in the unit cell. The equilibrium lattice parameters are computed to be a=b=3.15 Å and c=13.95 Å. The internal coordinates of Ta are determined to be (1/3, 2/3, 0.092). The band structure and density of states reveal that Ta₂AlC is an electronic conductor. The charge density distribution shows that the Ta and C atoms form a strong Ta-C-Ta covalently bonded chain.     

An extended ab initio study of the rotation-vibration spectrum of HOC+

Configuration interaction calculations have been performed in order to investigate the bending potential of the molecular ion HOC⁺ in detail. It is found that the bending potential has its minimum at the linear configuration and that it is very shallow. The ab initio points on the electronic ground state surface of HOC⁺ were combined with previously calculated points to determine an improved force field. This force field was used in the second-order rotation-vibration perturbation Hamiltonian, as well as in the semirigid bender Hamiltonian, to evaluate rotation and vibration frequencies of HOC⁺ and of some of its isotopes. The ν₀(J = 1?0) rotational transition frequency of the DOC⁺ isotope is predicted to be 76 200 ± 40 MHz.     

Covalency effects on implanted119Sn in group IV semiconductors studied by Mössbauer and channeling experiments

Radioactive^119mSn has been implanted with an isotope separator in single crystals of germanium, silicon, and diamond. Implantations of low doses (～10¹³ atoms/cm²) at room temperature were performed as well as of higher doses at temperatures of about 400°C. The Mössbauer spectra of these sources show mainly one line. This line originates from^119mSn on substitutional lattice sites as determined from channeling experiments with 2 MeV He⁺ ions on the same samples. The observed systematics of the isomer shifts for¹¹⁹Sn is explained on the basis of the average electronic configuration ns ^Z _snp ^Z _p characterizing chemical bonding in the host crystals. The Debye-Waller factors measured at room temperature are compared to values calculated in a high temperature approximation which accounts for impurity-host mass difference.     

Franck-Condon factor phase method for determining the potentials of bound states of piatomic molecules

A new method for determining a fragment of the potential function of a bound state of a piatomic molecule from the phase of the matrix element of an electronic transition is proposed. As opposed to the method of WKB nodes [Opt. Spektrosk. 83, 906 (1997)], the new method (we call it the Franck-Condon factor phase method) is suitable for analyzing only those spectral regions free from interference structures. However, it is less demanding to the quality of experimental data and makes it possible to study situations where only a portion of the electronic band profile is accessible for analysis. Accuracy characteristics of the method are demonstrated using the analysis of the spectra of the transitions in Na₂(2³Σ _g ⁺ (v=15, N=27; v=5, N=39)→³Σ _u ⁺ ) as an example.     

Hyperfine structure of ESR spectra as a probe for heisenberg exchange couplings in nitroxide triradicals serving as building blocks for molecule-based ferrimagnets

A study on electron spin resonance (ESR) spectroscopic determination of exchange interactions in organic oligoradicals is given. When the intramolecular exchange couplingJ between, unpaired electron spins in nitroxide-based oligoradicals falls within the order of 10 Oe (1 mK or 10^?3 cm^?1 forg=2), which is on the same order as the hyperfine couplingA of magnetic nuclei such as nitrogen atoms of nitroxide radicals, the magnitude ofJ can be determined from the hyperfine splitting pattern of ESR spectra in solutions. This range of the exchange couplingJ is not detectable in conventional magnetic susceptibility measurements. We demonstrate an application of hyperfine ESR spectroscopy as a probe for the exchange coupling to a series of organic oligoradicals, which the authors have recently developed as building blocks for molecule-based magnetic materials.     

Compton profiles of multiply ionized oxygen atoms

We have calculated Compton profiles of multiply ionized oxygen atoms with electronic configurations 1s^m2sⁿ2p^q, m=1−2,n=0−2,q=0−4. The values of the Compton profiles from the present calculation can be used to determine the doubly differential electron production cross sections in recent ion-atom collision experiments with oxygen ions in the rest frame of the target atoms. The calculations have been performed in impulse approximation using numerical Hartree-Fock wave functions. Compton profiles of neutral oxygen atoms, available in the literature, are in excellent agreement with the present calculation. The variation of Compton profile with the degree of ionization is investigated.     

Electronic transport properties of stuffed compositions of ferromagnetic copper chromium telluride: Cu1+xCr2Te4 (x=0-1)

We present here a detailed study of electronic transport properties of the metallic-ferromagnetic compounds Cu_1+xCr₂Te₄, having excess Cu atoms with x=0-1, from 2 to 400 K. The stuffing of the copper atoms in the parent structure reduces the ferromagnetic ordering temperature T_C from 325 to 156 K, while for the entire range the dependence of the electrical resistance and the thermopower with temperature and the anomalies in them on the magnetic ordering remain similar. All the compounds show a magnon-drag contribution in thermopower as a positive maximum around T_C/3, and a T² - dependence of resistivity at low temperatures. The increasing effects of the short range magnetic ordering in the paramagnetic resistivity are seen with the increase in the stuffing of atoms in these compounds. The transport properties are explained by the current carriers —the holes in a wide energy band dominated by the p-state of Te-atoms, which are scattered by the spindisorder in the paramagnetic phase and from the magnons in the ferromagnetic phase.     

Variation of electronic density in the superconducting phase transition in Nb<Subscript>3</Subscript>Al

The variation of electronic density in the superconducting phase transition in the classical superconductor Nb₃Al with critical temperature T_c=18.6 K was studied using ⁷³Ge emission Mössbauer spectroscopy. A comparison of the results obtained and the data available for the ⁶⁷Zn isotope in the lattices of high-temperature superconductors revealed a correlation between the electronic density variation at the Mössbauer probe nuclei sites and the value of T_c. This correlation is assumed to be related to the dependence of the electronic density variation on the standard correlation length.     

Determination of the isotope shift of115m Cd by a Zeeman scanning method

We have used an optical pumping-Zeeman scanning technique in order to determine the isotope shift in the 3,261 Å resonance line of 43-day, spin-11/2^115m Cd. A sample of ≈5×10¹² atoms was aligned in the¹ S ₀ diamagnetic ground state by optically pumping the sample with one selected Zeeman-scanned component of the³ P ₁?3,261 Å resonance line from a¹¹⁴Cd lamp. The alignment was detected through the modulation of the pumping beam at the nuclear resonance frequency. Thus by Zeeman scanning theF = 9/2 component of the³ P ₁ level and using previously determinedA- andB-values, we findδ5v(114–115m (9/2))= ?4,234(48) MHz and¹¹⁴Cd-^115mCd isotope shift = 87(48) MHz. We calculate a staggering parameterγ(^115mCd)=0.73(26), and a change in mean-square nuclear charge radiusδ〈r ²〉^114,115m =0.035(18)fm².     

A muonic X-ray study of the charge distribution of 144, 148, 150, 152, 154Sm

We report the measurement of the energies of the 4f → 3d, 3d → 2p and 2p → Is muonic atomic transitions in separated isotopes of ^{144, 148, 150, 152, 154}Sm, and that of the 2s → 2p transitions of ¹⁵²Sm as well. Using these transition energies as well as the hyperfine splittings of the 2p levels, we have interpreted our data in terms of a deformed Fermi distribution for the charge density and obtained good fits. A model independent analysis of the isotope shifts in terms of generalized R_h moments has been made and is in good agreement with electronic X-ray and optical isotope shifts. The static quadrupole moments and the isomer shifts of the first excited state of ^{152, 154}Sm have been determined from the 2p hyperfine structure.     

First-principles study on the structural and electronic properties of LiB and its hydrides (Li2BnHn, n=5, 8, 12, LiBH4)

Structural, electronic and vibrating properties of LiB and its hydrides (Li₂B_nH_n, n=5, 8, 12, LiBH₄) were calculated by the first-principles using density functional theory in its generalized gradient approximation. The calculated results are in good agreement with experimental studies. The deviation between theory and experimental results are also discussed. With the increasing of H atoms in range of 5-12, the band gap energy increases and the width of the conduction band decreases. Comparing with LiB, the band gap of LiBH₄ is broadened, which indicates the enhancement of Li-B and Li-H bond strength. Valence electrons mainly transfer from Li atoms to B and H atoms. As a result, Li atoms are thought to be partially ionized as Li⁺ cations. There is little contribution of Li orbital to the occupied states, resulting in Li-H and Li-B bond exhibiting an ionic nature, and B-H bond showing a covalent nature.