高密度氦相变的分子动力学研究

采用分子动力学方法结合对关联函数分析计算了0–1000 K范围内氦的固–液相变曲线, 与实验数据的对比显示, 在0–500 K之间与实验数据符合很好, 500 K以上还没有相应的实验数据. 另外, 计算了钛金属中不同尺寸氦泡的压强, 并与高密度氦的固–液相变曲线进行了对比. 结果显示, 在低温条件下, 随着温度的降低, 钛晶体中可能会出现固态氦泡; 在300 K以上不会存在固态氦泡.     

A high resolution study of 26Al via the (p,d) reaction

Excitation energies and angular distributions of ²⁶Al levels in the first 6 MeV of excitation have been measured with the ²⁷Al(p, d)²⁶Al reaction at E_p = 35 MeV. Deuteron spectra were analyzed with an Enge split-pole magnetic spectrograph and recorded on nuclear emulsions (experimental resolution ≈ 6 keV, FWHM); supplementary data were recorded with position-sensitive wire proportional counters. The angular distributions were analyzed with the DWBA to extract the l-values and associated spectroscopic factors of the neutron transfers. The results for excitation energies, l-values, spectroscopic factors, and values of J^π, T are discussed in terms of previous experimental and theoretical work and in the light of new shell-model calculations for this system.     

The effect of anti-hydrogen bond on Fermi resonance: A Raman spectroscopic study of the Fermi doublet ν1—ν12 of liquid pyridine

The effects of anti-hydrogen bond on the ν₁—ν₁₂ Fermi resonance (FR) of pyridine are experimentally investigated by using Raman scattering spectroscopy. Three systems, pyridine/water, pyridine/formamide, pyridine/carbon tetrachloride, provide varying degrees of strength for the diluent-pyridine anti-hydrogen bond complex. Water forms a stronger anti-hydrogen bond with pyridine than with formamide, and in the case of adding non-polar solvent carbon tetrachloride, which is neither a hydrogen bond donor nor an acceptor and incapable of forming hydrogen bond with pyridine, the intermolecular distance of pyridine will increase and the interaction of pyridine molecules will reduce. The dilution studies are performed on the three systems. Comparing with the values of Fermi coupling coefficient W of the ring breathing mode ν ₁ and triangle mode ν ₁₂ of pyridine at different volume concentrations, which are calculated according to the Bertran equations, in three systems, we find that the solution with the strongest anti-hydrogen bond, water, shows the fastest change in the ν₁—ν₁₂ Fermi coupling coefficient W with the volume concentration varying, followed by the formamide and carbon tetrachloride solutions. These results suggest that the stronger anti-hydrogen bond-forming effect will cause a greater reduction in the strength of the ν₁—ν₁₂ FR of pyridine. According to the mechanism of the formation of anti-hydrogen bond in the complexes and the FR theory, a qualitative explanation for the anti-hydrogen bond effect in reducing the strength of the ν₁—ν₁₂ FR of pyridine is given.     

Structural transition of Li3N under high pressure: A first-principles study

We theoretically study the electronic properties and pressure induced solid–solid phase transition of Li₃N by first-principles calculations. The calculations indicate a pressure-induced structural phase transition above 1.5GPa from the ambient $P6/MMM$ hexagonal phase (α-Li₃N) to a layered hexagonal phase (β-Li₃N, P63/MMC) which is accompanied by a 21.6% volume collapse. Above 38.8 GPa, β-Li₃N transforms into γ-Li₃N ($Fm\stackrel{?}{3}m$), and the recently reported new ${\alpha }^{\prime }$-phase ($P\text{-}3M1$) is not stable under high pressure. The analysis of electronic density of states suggests that various Li₃N polymorphs are insulators, and the band gap is broadened with further compression.     

Nanomechanics of single keratin fibres: A Raman study of the α‐helix →β‐sheet transition and the effect of water

The use of micro‐Raman spectroscopy, through chemical‐bond, nano‐scale probes, allows the changes in conformations (α‐helix →β‐sheet), chain orientation, breakage of disulfide bonds (20%) and the increase of intra‐ and inter‐chain distances during the application of stress to be distinguished. The combination of micro‐Raman spectroscopy and a Universal Fibre Tester allows a quantitative measurement of the extension of chemical bonds in the peptide chain during loading. The nano‐structural transformations of keratin during strain of human hair in a dry environment (40–60% relative humidity) and saturated with water have been studied. Water permits the sliding of the chains and decreases the bond energy of the hair. Spectral analyses and 2D correlation are two coherent and independent methods to follow the structural nano‐mechanical (Raman) and micro‐mechanical (strain/stress) analyses, and confirm the validity of the experimental results, tools and principles used, as well as the agreement with the structural model of keratin fibres described by Chapman and Hearle. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopic study on sodium hyaluronate: an effect of proton and γ irradiation

Raman spectroscopy was applied to the analysis of structural changes in lyophilised sodium hyaluronate after proton and γ irradiation (0.5, 5, 50, 100, 200 and 600 Gy). Characteristic Raman bands of the polysaccharide were sensitive to irradiation. Significant damage was observed at doses of 50 Gy or higher. The spectral changes confirmed radiation‐induced loss of native solution conformation, destruction of primary structure, fragmentation, cross‐linking and elimination of functional groups. Differences in the effects of proton and γ radiation on sodium hyaluronate are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Substitution and proton doping effect on SrZrO3 behaviour: high‐pressure Raman study

The high‐pressure Raman studies of pure, Yb‐modified, protonated and non‐protonated SrZrO₃ dense ceramics were performed between 0.1 and 40 GPa using a diamond anvil cell. Lanthanide‐modified, protonated SrZrO₃ perovskites are potential materials for electrolytic membrane in fuel cells and electrolysers working at medium temperature. The comparison of the Raman spectra shows important differences in the pressure behaviour between the pure and Yb‐modified SrZrO₃ ceramics. SrZrO₃ exhibits a rigid structure without any structural modification, whereas for both SrZr_0.93 Yb_0.07 O_2.965 and SrZr_0.93 Yb_0.07 O_2.962 H_0.003 a sequence of structural modifications at 10, 20 and 35 GPa is revealed. The character of these structural modifications is very similar to that observed as a function of the temperature (orthorhombic Pnma 750 °C → pseudo‐tetragonal Imma 840 °C → tetragonal I4/mcm 1070 °C → cubic Pm3m), which suggests that they can be considered as the phase transitions. Despite the low level of proton content (0.3% mole/mole), significant difference between protonated and non‐protonated compounds is observed for the 700–750 cm⁻¹ doublet assigned to the Zr O octahedron stretching mode, perturbed by an oxygen atom vacancy and/or neighbouring Yb ion. The location of proton is discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

A Raman scattering study of the phase transition in the (NH4)3WO3F3 oxyfluoride

The Raman scattering spectra of polycrystalline samples of the (NH₄)₃WO₃F₃ perovskite-like oxyfluoride were measured at frequencies of 70–3600 cm^?1 in the temperature range 93–323 K, including the transition from the orientationally disordered cubic phase to the low-symmetry phase. Transitional anomalies in the spectral parameters were revealed in the frequency ranges of internal vibrations of the ammonium ions and WO₃F₃ octahedral groups. An analysis of the experimental results allowed the conclusion that the phase transition under study is associated primarily with the ordering of the octahedral groups.     

Micro‐Raman study of PET single fibres under high hydrostatic pressure: phase/conformation transition and amorphization

The micro/nano structural evolution of a PET single fibre under hydrostatic pressure has been studied by Raman micro spectroscopy in a diamond anvil cell (DAC). Different bands in the Raman spectra were used as probes: the low wavenumber collective modes (<250 cm⁻¹) representative of the long‐range chain organization, as well as the stretching and bending amide and aromatic ring modes representative of the local chain behaviour. The in situ analysis at different pressures shows an evolution from an axial oriented trans‐conformation to an amorphous, isotropic material, i.e. the reverse transformation observed during the process of drawing the fibre from an isotropic amorphous precursor. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of chlorine substitution on triplet state structure of thioxanthone: A time‐resolved resonance Raman study

Substitution plays an important role in determining the triplet state reactivity. In this paper, we have studied the effect of chlorine substitution on the triplet state structure and the reactivity of thioxanthone (TX). We have employed time‐resolved resonance Raman technique to understand the structure of the lowest triplet excited state of 2‐chlorothioxanthone (CTX). The experimental findings have been corroborated with the computational results using density functional theory. Akin to the parent compound (TX), coexistence of two lowest triplet states has been observed in case of CTX, which has been substantiated using resonant probe wavelength dependence study. The relative contribution of ³n–π* to ³π–π* to the equilibrated triplet state has been found to be more for CTX compared to TX suggesting increase in the triplet state reactivity after the substitution. The above observation has been further supported by the flash photolysis experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization of the “native” surface thin film on pure polycrystalline iron: A high resolution XPS and TEM study

The characterization of the “native” surface thin film on pure polycrystalline iron has been studied by high resolution X-ray photoelectron (XP) spectroscopy of Fe 2p and O 1s regions. The film was allowed to form by exposing the sample to atmosphere at ambient conditions for a period of 1 h. The systematic approach used here includes the determination of curve fitting parameters from external standards and their use in fitting the raw data for the surface thin film. The quantitative high resolution XPS analysis involved an angle resolved study of the surface to determine the chemical composition and thickness of this native film. The film was found to be a mixture of Fe₃O₄ and Fe(OH)₂ with a thickness of 1.2 ± 0.3 nm. This conclusion is consistent with thermodynamics as indicated by the Pourbaix diagram for the Fe-H₂O system and the phase diagram for the Fe-oxygen system. A detailed TEM study of the native surface film also supports this conclusion.     

Raman spectroscopic study of serum albumins: an effect of proton‐ and γ‐irradiation

Raman spectroscopy was applied to analyse structural changes in serum albumins (bovine serum albumin, BSA; human serum albumin, HSA) following proton and γ‐irradiation (0.5, 5 and 50 Gy). Characteristic Raman bands of both polypeptide backbone and amino acid residues were sensitive to irradiation. Significant damage of HSA/BSA was observed only at the highest dose (50 Gy). Raman spectra confirmed radiation‐induced denaturation, destruction of helical structures and aggregation of serum albumins. The differences in the dose‐dependent effects of proton and γ‐radiation on studied proteins are discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

A high resolution neutron spectrometer for quasielastic scattering on the basis of spin-echo and magnetic resonance

We propose a high resolution neutron spectrometer, which combines the spin-echo principle with the separated coil magnetic resonance technique. The introduction of magnetic resonance instead of static spin-flippers in the spin-echo spectrometer allows the replacement of its high magnetic fields by low guide fields. The new technique represents a generalisation of the conventional spin-echo spectrometer.This property also holds for the double statistical-[8] the double Fourier- [9] and the Fotof-spectrometer [10], but those have not been built to our knowledge     

A high-resolution X-ray scattering study of the effect of defects on the first-order transition in KMnF3

A high-resolution X-ray scattering study of the influence of impurities on the cubic to tetragonal first-order phase transition of KMnF₃ is presented. It is shown that Ca⁺⁺ ions substituted for Mn⁺⁺ or Na⁺ ions substituted for K⁺ ions at a 1% concentration can influence drastically both the nature and the critical fluctuations of this transition. A qualitative attempt of interpretation in terms of random stress effects is presented.     

Deep UV resonance Raman spectroscopic study of CnF2n+2 molecules: the excitation of C–C σ bond

The σ–σ* transition of C–C bond in C_nF_2n+2 molecules was studied by deep UV resonance Raman spectroscopy. With the C–C σ bond selectively excited by the deep UV laser at 177.3 nm, the resonance Raman spectra of C_nF_2n+2 molecules were obtained on our home‐assembled deep UV Raman spectrograph. The Raman bands at 1299, 1380 and 2586 cm⁻¹ due to the C–C skeletal stretching modes are evidently enhanced owing to the resonance Raman effect. Based on the resonance Raman spectra and theoretical calculation results, it is proposed that the electronic geometry of C_nF_2n+2 molecules at the σσ* excited state is displaced along the directions perpendicular and parallel to the C–C skeleton, and the excited C–C bond is not dissociative due to the delocalization of the excited electron in σ* orbital. Copyright © 2012 John Wiley & Sons, Ltd.     

The effect of spectral resolution on the Raman spectra of polyaromatic hydrocarbons and beta‐carotene mixtures

The spectroscopic basis for extraterrestrial life‐detection through the molecular signatures of relevant biomaterials is dependent upon several instrumental facilities which could effect the diagnostic interpretation of key Raman bands from relevant substances occurring together in the geological record. To this effect, the Raman spectra of several polyaromatic hydrocarbons have been investigated under different conditions of spectral resolution using FT‐Raman‐spectroscopy operating at 1064 nm laser excitation wavelength. The observed Raman spectra are considerably altered under different conditions of spectral resolution; in particular, the discrimination between several polyaromatic hydrocarbons and beta‐carotene no longer becomes possible as the spectral resolution decreases. These results are relevant for the evaluation of miniaturised Raman spectrometers for space flight missions and incorporation into instrumentation for landers and rovers being proposed for future missions to Mars. Copyright © 2010 John Wiley & Sons, Ltd.     

UV resonance Raman study of TrpZip2 and related peptides: π‐π interactions of tryptophan

Aromatic interactions are important stabilizing forces in proteins but are difficult to detect in the absence of high‐resolution structures. Ultraviolet resonance Raman spectroscopy is used to probe the vibrational signatures of aromatic interactions in TrpZip2, a synthetic β‐hairpin peptide that is stabilized by edge‐to‐face and face‐to‐face tryptophan π‐π interactions. The vibrational markers of isolated edge‐to‐face π‐π interactions are investigated in the related β‐hairpin peptide W2W11. The bands that comprise the Fermi doublet exhibit systematic shifts in position and intensity for TrpZip2 and W2W11 relative to the model peptide, W2W9, which does not form aromatic interactions. Additionally, hypochromism of the B_b absorption band of tryptophan in TrpZip2 leads to a decrease in the relative Raman cross‐sections of B_b‐coupled Raman bands. These results reveal spectral markers for stabilizing tryptophan π‐π interactions and indicate that ultraviolet resonance Raman may be an important tool for the characterization of these biological forces. Copyright © 2012 John Wiley & Sons, Ltd.