NMR relaxation of 7Li in concentrated lithium-ammonia solutions

The Knight shift and the spin-lattice relaxation time of ⁷Li in lithium-ammonia solutions have been measured at -57°C over the concentration range X_Li = 0.01–0.20 (X_Li: mole fraction of Li). The Knight shift increases with increasing metal concentration, while the relaxation rate, 1/T₁, shows a broad minimum around X_Li = 0.07.     

Different electronic structures of C6Li and C8K graphite intercalation compounds studied by positron annihilation

The 2λ-angular correlation distributions of the stage 1 Graphite Intercalation Compounds C₆Li and C₈K are found to be very different. For C₈K, the distributions are dominated by a free electron contribution similar to those in pure alkali metals. In contrast, the distributions of C₆Li remain similar to those of graphite. The two materials are classified into s(+ π)-band metals (C₈K) and π-band metals (C₆Li).     

Modulation of the work function of fullerenes C60 and C70 by alkali-metal adsorption: A theoretical study

The impact of alkali-metal (Li/Na/Cs) adsorption on work function of fullerenes C₆₀ and C₇₀ was investigated by first-principles calculations. After adsorption, the work functions of fullerenes C₆₀ and C₇₀ decrease distinctly and vary linearly with the electronegativity of the alkali metal elements, and the positions where the alkali atoms are adsorbed considerably influence the work functions. On the contrary, a vacancy defect elevates the work functions of the fullerenes C₆₀ and C₇₀. The variation in the work functions rests with variation in Fermi level (which are attributed to charge transfer) and variation in vacuum levels (which are attributed to the induced dipole moments). Moreover, alkali-metal adsorption can also improve the electric conductivity of a fullerene mixture of C₆₀ and C₇₀.     

C2和C2+,C2-的电子结构与势形共振

本文在独立电子近似的基础上,根据多重散射自洽场理论方法,计算了C₂和C₂⁺,C₂^-分子(离子)的电子结构,阐明了势形共振能量和上述分子(离子)电子数的关系,结果表明,随着电子数的减少,C原子2s-2p轨道杂化减弱,势形共振的能量将降低(如降低到阈值下,则势形共振消失)。 关键词：     

23Na Knight shift of liquid Na-Sn alloys

Measurements of the ²³Na Knight shift in liquid Na-Sn alloys provide strong indications for the formation of compounds about the two distinct compositions Na₄Sn and Na₄Sn₃.     

High resolution NMR in metallic samples of 27Al and 9Be

Four-pulse experiments have been performed on ²⁷Al and ⁹Be in metallic powder samples. A line narrowing effect was achieved, which resulted in a symmetric line of about 200–300 Hz half width in both cases. No anisotropy was observed, but refined values of the Knight shift were obtained: 1636 ± 3 ppm for ²⁷Al and - 10.0 ± 3 ppm for ⁹Be.     

Rotational spectra of the deuterated carbon chain molecules: C3D, C4D, C3HD, and C4HD

The rotational spectra of the deuterated carbon chain molecules, C₃D, C₄D, C₃HD, and C₄HD, have been measured with the Fourier transform microwave (FTMW) spectrometer. The C₃D and C₄D radicals are produced by discharging the DCCD gas diluted in Ar. On the other hand, the gaseous mixture of HCCH, DCCD, and HCCD diluted in Ar is used for producing C₃HD and C₄HD. For C₃D, the molecular constants are determined from a joint least-squares analysis with the previously published millimeter- and submillimeter-wave data by considering the vibronic interaction between the ²Π ground state and the low-lying ²Σ vibronic state. The molecular constants of C₄D are determined by use of the conventional Hamiltonian of the ²Σ radical, while the effective rotational constant and centrifugal distortion constant are derived for C₃HD and C₄HD. In the present study, the hyperfine interaction constants of the deuterium nuclei in C₃D and C₄D are determined accurately. In particular, the nuclear quadrupole interaction constant, eQq, of the C₃D radical is found to be significantly smaller than those of C₂D and C₄D, indicating that C₃D has a floppy motion of the CCD bending mode due to the large Renner-Teller effect.     

Absorption spectra of C6H6 and C6D6 near 340 nm

The absorption spectra of C₆H₆ and C₆D₆ in the liquid phase have been studied near 340 nm. The absorption spectrophotometric mounting was a sequential double-beam attachment with linear response to energy on scanning of the spectrum before the exit slit and an electronic device which gives directly either the absorbance or the integrated absorbance of a transition and, consequently, its oscillator strength.The oscillator strength measured for the band of C₆H₆ is 8×10^?8, which corresponds to a dipole moment of 2.4×10^?3 Debye; this value is of the same order as a theoretical value calculated by Tsubomura and Mulliken (3.8×10^?3 Debye) for a transition between states ³F and ³A of an oxygen-benzene pair. This agreement corroborates the hypothetical existence of such a transition.The first vibrational band is at 28553 cm^?1 for C₆H₆; this band is not observed in the vapor or solid phase. It corresponds probably to the transition 0-0, which is considered in the literature to be near 29500 cm^?1. The isotopic shift measured for this first band is 164 cm^?1. The vibrational frequencies are, respectively, 910 cm^?1 for C₆H₆ and 889 cm^?1 for C₆D₆.     

1H chemical shift tensor in squaric acid: C4O4H2

The proton chemical shift tensor in squaric acid, which undergoes an antiferrodistortive phase transition at T_c = 97°C, has been determined by means of a multiple-pulse NMR experiment. No change of the shift tensor is observed, when going through the phase transition, indicating a purely order—disorder type transition. The principal values of the shift tensor are: — 26.5, —20.2 and 1.0 ppm with respect ti TMS.     

Geometric shielding corrections for total cross section calculations of electron scattering by CH4, C2H6, C2H3F3, C2H4, C2F4, C2Cl4 and C2Cl2F2 from 30–5000?eV

To quantify the changes in the geometric shielding effect in a molecule as the incident electron energy varies, an empirical fraction, which represents the total cross section contributions of shielded atoms in a molecule at different energies, is presented. Using this empirical fraction, the total cross sections for electron scattering by CH₄, C₂H₆, C₂H₃F₃, C₂H₄, C₂F₄, C₂Cl₄ and C₂Cl₂F₂ are calculated over a wide energy range from 30 to 5000 eV by the additivity rule model at the Hartree-Fock level. The quantitative total cross sections are compared with those obtained by experiment and other theories where available. Good agreement is attained above 100 eV.     

dt, d3He, and pα scattering in the vicinity of the 5He* and 5Li* resonances

It is shown that the simplest strong-interaction models (those that employ the Breit boundary condition and a delta-function potential) involving only three free parameters describe adequately the properties of the dt and d ³He systems in the vicinity of the ⁵He*(3/2⁺) and ⁵Li*(3/2⁺) resonances—that is, at energies in the regions E≲3E _C and E≲2E _C where E _C is the corresponding Coulomb energy. For these systems, the complex values of the scattering length, of the effective range, and of the shape parameter are extracted from experimental data on the reaction cross section and proton polarization in pα scattering (in the case of the d ³He system). The astrophysical function is extrapolated to the low-energy region (0≤E<0.1E _C), which is of importance for thermonuclear investigations, but which is hardly accessible to direct measurements. __________ Translated from Yadernaya Fizika, Vol. 66, No. 1, 2003, pp. 89–99. Original Russian Text Copyright ? 2003 by Kulik, Mur.     

The 209B Knight shift in the semiconducting liquid Bi-Te system

Measurements of the Knight shift of ²⁰⁹Bi in liquid Bi-Te are reported for the entire concentration range at elevated temperatures (600–12000 K). Our results give additional support to the assupmtion that in the liquid phase Bi₂Te₃ bonds are still present. The measurements can be interpreted in the frame of Mott's pseudogap model.     

Scanning tunneling microscopy of surface-adsorbed fullerenes: C60, C70, and C84

Scanning tunneling microscopy (STM) is used to characterize partial monolayers of C₆₀, C₇₀, and C₈₄ adsorbed on the Au(1 1 1) surface at room temperature and under ambient conditions. A high degree of structural polymorphism is observed for monolayers of each of these fullerenes. For C₆₀, three lattice packings are observed, including a previously unreported 7 × 7 R21.8° structure that is stabilized by adjacent surface step defects. For C₇₀, two lattice packings are observed, and analysis of molecular features in STM images allows molecular binding geometry to be determined. In one of the two observed lattice structures, C₇₀ molecules align their long axis along the surface normal, while in the other, molecules align parallel to the surface and along a gold lattice direction. The parallel geometry is also preferred for isolated and loosely packed molecules on the surface. C₈₄ exhibits a large number of lattice orientations and no long-range order, and likely binds incommensurately on Au(1 1 1). Time series of images of partial C₇₀ monolayers show progressive surface modification as a result of perturbation by the STM tip; this is in contrast to the behavior of C₆₀, where alterations in surface structure at room temperature are thermally driven.     

Low-lying 134Cs excited states from the (n, γ) reaction

Low-energy γ-ray and conversion electron spectra from the ¹³³Cs(n,γ)¹³⁴Cs reaction have been investigated with a bent cyrstal spectrometer, β-speetrometer, Ge(Li) and Si(Li) detectors. Gamma-gamma coincidence measurements were made with the Ge(Li)-Ge(Li) arrangement. Gamma-gamma delayed coincidences have been studied with the use of the Ge(Li)-NaI(Tl) coincidence set-up. The decay of 2.9 h ^134mCs has been investigated with the prism β-spectrometer and Ge(Li) detector. The half-lives of the 176.403 and 257.112 keV levels have been measured to be 49.7 ± 0.8ns and 12.3 ± 1.1 ns respectively. The neutron binding energy B_n have been calculated to be 6891.4 ± 1.3 keV. Spin and parity assignments have been made for almost all the levels. The possible structure of the levels deduced is discussed.     

EXTENDED SSH MODEL FOR C58B2 AND C58N2

The extended Su-Schrieffer-Heeger model is used to study the electronic energy levels and molecular structures for two kinds of isomers of C₅₈X₂(X=B, or N). In each case we obtain two sets of stable solutions. For C₅₈X₂ (1, 2), both sets of solutions are found to be reasonable, indicating two different phases. For C₅₈X₂(1, 60 ), only one set of solutions which satisfy the central inversion symmetry is physically reasonable.     

Pressure broadening and collisional shift of the Rb D2 absorption line by CH4, C2H6, C3H8, n-C4H10, and He

The pressure broadening and shift rates of the rubidium D2 absorption line 5²S_1/2→5²P_3/2 (780.24 nm) with CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He were measured for pressures ≤80 Torr using high-resolution laser spectroscopy. The broadening rates γ_B for CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He are 28.0, 28.1, 30.5, 31.3, and 20.3 (MHz/Torr), respectively. The corresponding shift rates γ_S are −8.4, −8.8, −9.7, −10.0, and 0.39 (MHz/Torr), respectively. The measured rates of Rb for the hydrocarbon buffer gas series of this study are also compared to the theoretically calculated rates of a purely attractive van der Waals difference potential. Good agreement is found to exist between measured and theoretical rates.     

Carbon K-shell excitation of C2H2, C2H4, C2H6 and C6H6 by 2.5 keV electron impact

Energy loss spectra of 2.5 keV electrons in the region of the carbon K-edge in C₂H₂, C₂H₄, C₂H₆ and C₆H₆ are report     

Neutron-induced charged-particle reactions in 6Li and 9Be

Angular distributions of tritons from the ⁶Li(n, t)⁴He reaction were measured at E_n = 7.25, 6.77, 6.57, 5.24 and 4.71 MeV. Angular distributions of douterons from respectively, the ⁶Li(n, d)⁵He two-body breakup reaction were measured at E_n = 6.77 and 6.57 MeV, and of protons from the ⁶Li(n, p)⁶He reaction at E_n = 6.77, 5.24 and 4.71 MeV. All these reactions in ⁶Li were analyzed as direct interaction in the formalism of the distorted wave Born approximation. The optical model for the nuclear interaction was found to apply reasonably well to nuclei as light as ⁴He, ⁵He, ⁶He and ⁶Li. In addition, ⁶Li as an alpha-deuteron cluster gives the best bound-state wave function to describe the experimental angular distribution of tritons. The excitation functions at forward angles of the ⁶Li(n, t)⁴He, ⁶Li(n, d)⁵He and ⁶Li(n, p)⁶He reactions were measured for incident neutron energies between 4.4 and 7.3 MeV. It is found that the ⁶Li(n, d)⁵He two-body breakup reaction has a threshold at about E_n = 5.3 MeV. Angular distributions at E_n = 18.3 MeV for tritons and protons from the ⁹Be(n, t)⁷Li and ⁹Be(n, p)⁹Li, respectively, were also measured.     

The electron capture decay of 131Ba

The decay of ¹³¹Ba has been investigated by means of a 4π internal source scintillation spectrometer and a Ge(Li) detector. The L/K. and M/L electron capture ratios of the allowed transitions to the 373, 620 and 1048 keV levels in ¹³¹Cs have been measured. From these electron capture ratios, the ifQ_EC value and the exchange and overlap corrections X^L/K and X^M/L have been derived.     

C59N和C19N晶体的合成

通过溶解C₆₀的CCl₄溶液在大气中的慢蒸发可以合成C₅₉N和C₁₉N晶体,这项实验结果为C_nN（n≤59）晶体研究开辟了一种简单而有效的途径. 关键词： 富勒烯晶体 飞行时间质谱 透射电子显微镜 X射线光电子能谱