Magnetic shielding and spin-rotation interaction in ground state alkali molecules

Precision measurements of nuclear magnetic dipole moments in alkali molecules are performed using atom-molecule exchange optical pumping. A comparison with measurements on alkali atoms gives the magnetic shielding differences between atoms and molecules and an approximate value for the spin-rotation interaction constant of the alkali molecules. It is reported on experiments on³⁹K₂ and⁸⁷Rb₂.     

Magnetic studies with zero field NMR

A review is given of the information about a ferromagnetic system obtainable from swept frequency NMR. The distinction between signals from nuclei in domains and domain walls is stressed and recent advances in instrumentation described.     

NMR on alkali fullerides

NMR results concerning the electronic and the molecular dynamic properties of alkali fullerides are presented and discussed. The dynamics as observed in line width and spin-spin relaxation is similar for A₄C₆₀ and A₃C₆₀. Spin-lattice relaxation and line shift depend strongly on the electronic properties and differ considerably for the various alkali concentrations.     

Fullerene local order in Na2CsC60 by23Na NMR

We have investigated the alkali metal fulleride Na₂CsC₆₀ by²³Na nuclear magnetic resonance (NMR), The NMR line of the tetrahedral site is split below 170 K (T and T′ lines) similarly to the A₃C₆₀ compounds with A=Rb or K. The intensity fraction of the T′ line follows the same temperature dependence as the¹³C NMR line width. We have also found that the spectrum is independent of the cooling rate. Spin-echo double resonance measurements show that T and T′ sites are mingled on a microscopic scale. We propose that the different²³Na NMR lines correspond to different fullerene orientational environments of the tetrahedral alkaline site.     

Cs2分子的光解离和碰撞能量转移

利用He-Cd+激光器的441.6 nm线光解Cs2分子,使Cs(6D)态得到布居,在Cs2密度为1～9×1015 cm-3范围内,测量原子荧光对分子荧光强度比,得到碰撞转移率系数对解离率之比为9.6×10-18 cm3.测定Cs(6D3/2)对6D5/2荧光强度分支比,得到62D态精细结构能级解离率之比为0.41.从翼激发得到的精细结构转移截面与从共振激发得到的截面结果相符.     

Magnetic shielding of23Na nuclei in NaNO3 and NaBrO3 single crystals

Single crystals of sodium nitrate, sodium chlorate and sodium bromate were investigated by continuous wave and Fourier transform pulse techniques. The sodium shielding tensors for studied compounds were found from the shift of the central line of²³Na triplet, which was measured as a function of the crystal orientation. The shielding appears isotropic in NaNO₃ and anisotropic in chlorate and bromate salts; the anisotropies are 0±2, 12±1 and 17±1 ppm respectively. It is suggested that lattice forces lowering the local symmetry at the sodium site are responsible for the observed effects of shielding anisotropy.     

Thermal averaging of the spin-rotation coupling in small molecules leads to an isotropic NMR shielding

It has been known for over 70 years that nuclear spins couple to molecular rotation via a Zeeman interaction. This spin–rotation coupling can be observed as a discrete splitting in molecular beam magnetic resonance experiments, but is quenched by molecular collisions at higher pressures. We show that because of differential thermal population of M_J levels at high magnetic fields, the spin rotation coupling retains a small isotropic component at high field. For all but the smallest molecules at very low temperature, the residual coupling is temperature independent and linear in the magnetic field; it therefore closely mimics the chemical shift. The ‘super spin rotation’ shift may in the future be a necessary correction to ultra – high precision computations of the NMR chemical shielding of small molecules in gases and liquids.     

Charge density wave transition in Na2Ti2Sb2O probed by 23Na NMR

Herein we investigated the electronic properties of layered transition-metal oxides Na2Ti2Sb2O by23Na nuclear magnetic resonance(NMR)measurement.The resistivity,susceptibility and specific heat measurements show a phase transition at approximately 114 K(TA).No splitting or broadening in the central line of23Na NMR spectra is observed below and above the transition temperature indicating no internal field being detected.The spin-lattice relaxation rate divided by T(1/T1T)shows a sharp drop at about 110 K which suggests a gap opening behavior.Below the phase transition temperature zone,1/T1T shows Fermi liquid behavior but with much smaller value indicating the loss of large part of electronic density of states(DOS)because of the gap.No signature of the enhancement of spin fluctuations or magnetic order is found with the decreasing temperature.These results suggest a commensurate charge-density-wave(CDW)phase transition occurring.     

Magnetic properties and Fe NMR studies of U-type hexaferrites

U-type hexaferrites with compositions Ba₄Me₂Fe₃₆O₆₀ (Me=Cu, Fe, Co, Mn and Mg) have been synthesized and characterized by magnetization measurements and zero field ⁵⁷Fe nuclear magnetic resonance (NMR) spectra. The NMR spectra show resonance peaks corresponding to different crystallographic sites of iron (tetrahedral, octahedral and trigonal bipyramidal) with integral intensities according to their site multiplicity. In comparison with the NMR spectrum of M-type barium hexaferrite the intensities of some of the peaks arising due to iron sublattices (f_IV, a and b sites) are different, though there is no difference in peak positions indicating the same local hyperfine field strength at Fe nuclei. The maximum saturation magnetization at room temperature was found in Cu₂U (70 emu/g) and Fe₂U (67 emu/g). The Curie temperatures, saturation magnetizations and coercitivities for the U-type hexaferrites are given.     

Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR

Through 13C NMR spin lattice relaxation ( T1) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and strong electronic correlations must be considered to understand the behavior of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR, implying the occurrence of excitations typical of JT distorted C( 2-)60 (or equivalently C( 4-)60). This supports the idea that dynamic JTD can induce attractive electronic interactions in odd electron systems.     

Deuterium NMR and ab initio studies of strongly hydrogen-bonded molecules

Two newly synthesized alkylated cyanomalonaldehyde derivatives possess very short intramolecular hydrogen bonds, which are studied by deuterium NMR. Both the dimethyl and di-tert-butyl derivatives have small deuterium quadrupole coupling constants and large asymmetry parameters. In addition, the di-tert-butyl compound, which has one of the shortest O D...O hydrogen bonds yet measured, has a quadrupole coupling which anomalously increases with temperature. The significance of these phenomena is explored using a theoretical model which employs vibrationally averaged ab initio electric field gradient tensors calculated with large basis sets and electron correlation via the multiconfigurational self-consistent field method.     

Coupled cluster study of NMR shielding constants and spin-rotation constants in SiH4, PH3 and H2S molecules

Ab initio methods are applied to analyse the NMR shielding constants and spin-rotation constants in SiH₄, PH₃ and H₂S molecules. The electron correlation effects are studied applying the MP2 and coupled cluster perturbation approaches. The basis set convergence is examined at the same time, and the final results for the equilibrium geometries are obtained at the CCSD(T)/cc-pCVQZ level. Zero-point vibrational and temperature contributions are computed at the SCF, MP2 and CCSD level of approximation. In addition, for the shielding constants we also estimate the relativistic effects, to determine total values of the shielding of the third-row nuclei in the studied molecules. Our final results for the shielding constants at 300?K are σ (²⁹Si in SiH₄)?=?482.35?ppm, σ (³¹P in PH₃)?=?611.64?ppm and σ (³³S in H₂S)?=?736.13?ppm. These values, together with estimated corrections and error bars, can be used to determine absolute NMR shielding scales for the heavy nuclei.     

Spectroscopic studies of NaCs for the ground state asymptote of Na + Cs pairs

The ground state X of NaCs was studied by laser induced fluorescence Fourier-transform spectroscopy. An accurate potential energy curve was derived from more than 5000 transitions. This potential reproduces the experimental observations within their uncertainties of cm^-1 and covers about 99.97% of the potential well depth. Few vibrational levels of the shallow state a below the atomic ground state asymptote were observed. The identification is mainly done by the observed and quantitatively interpreted molecular hyperfine structure applying atomic parameters of the ground states of Na and Cs. An estimated potential curve for a is reported which can be used together with that of X for coupled channel calculations of cold collisions between Na and Cs. An example is given. Electronic supplementary material to this article is available at and is accessible for authorized users. Received: 10 September 2004, Published online: 23 November 2004 PACS: 31.50.Bc Potential energy surfaces for ground electronic states - 33.20.Kf Visible spectra - 33.20.Vq Vibration-rotation analysis - 33.50.Dq Fluorescence and phosphorescence spectra Supplementary tables (Tabs. I-III) are only available in electronic form at http: //www.eurphysj.org     

Optical properties from time-dependent current-density-functional theory: the case of the alkali metals Na,K, Rb,and Cs

We present the optical conductivity as well as the electron-energy loss spectra of the alkali metals Na, K, Rb, and Cs calculated within time-dependent current-density functional theory. Our ab initio formulation describes from first principles both the Drude-tail and the interband absorption of these metals as well as the most dominant relativistic effects. We show that by using a recently derived current functional [Berger, Phys. Rev. Lett. 115, 137402 (2015)] we obtain an overall good agreement with experiment at a computational cost that is equivalent to the random-phase approximation. We also highlight the importance of the choice of the exchange-correlation potential of the ground state.     

Simplified SCF calculations on the diatomic alkali metal molecules

An account is given of a new formalism for calculating energy levels in molecules using techniques that derive from the band theory of metals. After showing how the molecular potential may be transformed into a cellular potential we define the basis set of muffin-tin orbitals and discuss some of their properties. The relationship between the scattered wave formulation of Johnson, which is restricted to muffin-tin potentials, and our more general approach based on the use of a linear combination of muffin-tin orbitals (L.C.M.T.O.) is explicitly indicated. We then show how the properties of the muffin-tin orbitals, together with the technique of cellular integration, give rise to a hamiltonian matrix. This matrix is as general as, but simpler than that obtained by the use of atomic orbitals, and it is linear in energy and therefore computationally faster than the secular matrix of the scattered wave method.     

Magnetic structure of low-dimensional LiCu2O2 multiferroic according to 63,65Cu and 7Li NMR studies

The complex NMR study of the magnetic structure of LiCu₂O₂ multiferroic has been performed. It has been shown that the spin spirals in LiCu₂O₂ are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu²⁺ chains. A magnetic field of H ₀ = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H ₀ ?? b.     

23Na NMR in the relaxor ferroelectric Na1/2Bi1/2TiO3

The ²³Na NMR spectra of a Na_1/2Bi_1/2TiO₃ crystal are studied at frequencies of 79.4 and 15.7 MHz in the temperature range 150–720 K. It is revealed that, at all temperatures, the crystal contains regions with a nearly cubic matrix and polar clusters. The temperature dependence of the local distortion of the Na environment in the clusters is determined. The dynamics of the reorientation of the local cluster polarization in the tetragonal and trigonal NBT phases is analyzed.