Muon spin relaxation measurements of CsC60, RbC60, KC60

Muon spin relaxation (μ⁺SR) measurements of CsC₆₀ and RbC₆₀ have revealed magnetic ordering at 20 K and 15 K respectively, with static internal fields at the muon site of \sim7 G for both samples. No magnetic ordering is seen in KC₆₀ down to 2.5 K. An apparent small increase in muon spin relaxation which had been seen at 70 K in RbC₆₀ is ascribed to an extrinsic effect, originating in muons which stopped in the aluminum sample holder. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relativistic electronic structure calculations on endohedral Gd@C60, La@C60, Gd@C74, and La@C74

We have investigated the adsorption of Ba on the Si(111) surface at elevated temperatures by using high-resolution electron-energy-loss spectroscopy, low-energy-electron diffraction, and photoelectron spectroscopy with synchrotron photons. We found two new ordered phases 2×1a and 2×1bwith increasing Ba coverage in addition to other ordered phases reported earlier. All the ordered surfaces were found to remain semiconducting with a hybridization band gap of ∼1.1 eV almost independent of Ba coverage. We discuss evidence for the evolution of a Ba s-s hybridization band for Ba coverage beyond 0.5 monolayers and propose structural models for the three ordered phases, which are quite consistent with our experimental data. Received: 16 May 2000 / Accepted: 17 May 2000 / Published online: 16 August 2000     

C60、C60F60及C60H60“分子滚珠”的压缩特性与电子结构

采用量子分子动力学技术,模拟了C60、C60F60与C60H60分子的压缩过程,计算了这些"分子滚珠"受压变形后的电子结构.根据计算结果,对比、分析了三种分子的压缩力学特性以及压缩变形对其电子结构的影响.研究表明,1)三种分子的抗压缩载荷与能量吸收能力有C60F60＞C60H60＞C60的排序,但抗变形能力相当;2)随着压缩变形的增大,三种分子的化学活性增加,但相同应变下,C60F60和C60H60分子有着比C60更好的化学稳定性.     

Theoretical thermochemistry of the C60F18, C60F36, and C60F48 fluorofullerenes

Relative energies of C₆₀F_N fluorofullerenes are reproduced reasonably well at the B3LYP/6- 311G** level of theory employed in conjunction with isodesmic transfluorination reactions, although overestimation of steric repulsions among non-bonded atoms is evident for species with larger values of N. On the other hand, the MNDO method is found to be less suitable for studies of fluorofullerene thermochemistry. The gas-phase standard enthalpy of formation of the C₆₀F₁₈ species is predicted to lie between ?1500 kJ mol^?1 and ?1400 kJ mol^?1.     

87Rb NMR investigations on binary and ternary fullerene compounds: Rb3C60, K2RbC60 and Rb2CsC60

Results of¹³C MAS NMR and⁸⁷Rb NMR measurements on Rb₃C₆₀, K₂RbC₆₀ and Rb₂CsC₆₀ are presented. The⁸⁷Rb NMR spectra show generally the same characteristics as already reported by other authors. For the ternary compound the degree of site preferential order of the alkali metal ions agrees with the analysis of X-ray absorption data. Furthermore, in the room temperature⁸⁷Rb NMR spectra of all samples an additional broadened line is detected indicating that at least for the samples prepared from sublimed C₆₀ a considerable amount of the Rb ions is located on sites with symmetry lower than cubic.     

Electron attachment to doped helium droplets: C60 -, (C60)2 -, and C60D2O- anions

Helium nanodroplets, formed in a supersonic expansion, are doped with C₆₀ in a pickup cell. In some experiments, they are co-doped with water. Electrons are attached to the doped droplets; the yield of anions is recorded as a function of electron energy. The C₆₀ ^- yield extends to much higher energies than in experiments involving isolated, hot fullerenes; we attribute the difference to the low temperature of the neutral precursors and the efficient cooling of the nascent anions by the helium droplet, which quench thermally activated autodetachment. The yields of (C₆₀)₂ ^- and C₆₀D₂O^- anions reveal another important factor, namely depletion of the anion signal by dissociation which is energetically more facile than autodetachment.     

Ar 原子内嵌对C60 富勒烯碰撞的影响

基于半经验势的分子动力学模型， 研究了相同能量下 C₆₀ +C₆₀ 与 Ar@C₆₀ +Ar@C₆₀ 的对心碰撞后形成的富勒烯结构的不同。 发现在相同的能量下， Ar@C60 +Ar@C60 形成的碰撞产物的结构相比 C₆₀ +C₆₀ 碰撞产物的结构有着明显的不同: 前者形成“花生”状的新富勒烯结构， 后者形成“哑铃”状的双富勒烯结构。     

C60、C240、C60@C240富勒烯分子压缩特性的分子动力学研究

采用Tersoff-Brenner势的分子动力学方法,研究了双石墨层作用下C60、C240及C60@C240富勒烯分子的压缩力学特性.根据计算结果,讨论了三种分子压缩过程中几何构形、能量、压缩载荷等的变化及其差异.研究表明,压缩过程中,仅C240分子出现了“塌陷“现象,塌陷时,该分子的能量及外载一度下降;相同压缩应变下,C240的体积压缩率以及C60@C240的能量吸收率最大,而C60的体积压缩率及能量吸收率均最小; C60@C240分子的最大承载能力及C240的最大承受变形能力最大,而C60分子的最大承载和最大承受变形能力均最小;在C60@C240分子的压缩中,当应变小于20%时,内笼C60的体积及其能量变化很小;C60与C240之间的范德华尔能在整个压缩C60@C240分子的能量变化中仅仅占有非常小的份额.     

Theoretical study on the mono and multiply oxygenated Si60H60 fullerene

We have applied density functional theory (DFT) calculations to study the structures, stabilities, electronic and magnetic properties of mono and multiply oxygenated Si₆₀H₆₀ fullerenes (Si₆₀H_60–2nO_n, n = 1, 3, 6, 9, 10, 12, 18, 20, 21, 27 and 30). DFT results show that rearrangement between the closed [6,6] and [5,6] isomers of Si₆₀H₅₈O follows a two-step pathway involving an intermediate and two transition states. Preserving the C₃ symmetry in the cage structure, extra epoxidation of Si₆₀H₆₀ has been accomplished. Based on our results, formation energies per oxygen atom for the multiple additions of oxygen atoms on Si₆₀H₆₀ cage are positive (endothermic character), and increase with the increasing of the number of oxygen atoms. In general, the oxygenation of Si₆₀H₆₀ cage leads to an increase in the electrophilicity of the Si₆₀H_60–2nO_n oxides. The oxygenation of Si–Si bonds not only introduces a substantial broadening of the NMR pattern but also yield individual peaks, indicating different electrostatic environments of silicon nuclei in the Si₆₀H_60–2nO_n oxides.     

In-flight radiation measurements on STS-60

A joint investigation between the United States and Russia to study the radiation environment inside the Space Shuttle flight STS-60 was carried out as part of the Shuttle-Mir Science Program (Phase 1). This is the first direct comparison of a number of different dosimetric measurement techniques between the two countries. STS-60 was launched on 3 February 1994 in a nearly circular 57 degrees x 353 km orbit with five U.S. astronauts and one Russian cosmonaut for 8.3 days. A variety of instruments provided crew radiation exposure, absorbed doses at fixed locations, neutron fluence and dose equivalent, linear energy transfer (LET) spectra of trapped and galactic cosmic radiation, and energy spectra and angular distribution of trapped protons. In general, there is good agreement between the U.S. and Russian measurements. The AP8 Min trapped proton model predicts an average of 1.8 times the measured absorbed dose. The average quality factor determined from measured lineal energy, y, spectra using a tissue equivalent proportional counter (TEPC), is in good agreement with that derived from the high temperature peak in the 6LiF thermoluminescent detectors (TLDs). The radiation exposure in the mid-deck locker from neutrons below 1 MeV was 2.53 +/- 1.33 microSv/day. The absorbed dose rates measured using a tissue equivalent proportional counter, were 171.1 +/- 0.4 and 127.4 +/- 0.4 microGy/day for trapped particles and galactic cosmic rays, respectively. The combined dose rate of 298.5 +/- 0.82 microGy/day is about a factor of 1.4 higher than that measured using TLDs. The westward longitude drift of the South Atlantic Anomaly (SAA) is estimated to be 0.22 +/- 0.02 degrees/y. We evaluated the effects of spacecraft attitudes on TEPC dose rates due to the highly anisotropic low-earth orbit proton environment. Changes in spacecraft attitude resulted in dose-rate variations by factors of up to 2 at the location of the TEPC.     

A note on60Co decay

Theγ-rays from⁶⁰Co have been studied with a 30 cm³ Ge(Li) detector. Gamma rays of energies 826.4 and 2,158.9 keV which are expected on the basis of the⁶⁰Co decay scheme were sought but not observed. Their intensities are <0.02% and <0.002%, respectively, of the⁶⁰Co disintegrations. Any direct feeding from the (5⁺)⁶⁰Co ground state to the (2⁺) 2,159 keV level is <0.022%, yielding a logft>12.3 for the 664 keV second-forbidden uniqueβ-transition. Radioactivity⁶⁰Co; measuredE _γ,I _γ.⁶⁰Ni deduced levels, logft. Ge(Li) detector.