Molecular dynamics simulations of binary mixtures of methane and hydrogen in zeolite A and a novel zinc phosphate

Molecular dynamics simulations have been used to study binary mixtures of hydrogen and methane in two molecular sieve structures, zeolite NaA and a novel zinc phosphate molecular sieve, Na₃ZnO(PO₄)₃, which has a pore size tuned to light gas separations. Simulations were run at high temperature, T = 500 °C. Equimolar mixtures of methane and hydrogen in both molecular sieve structures were simulated at loadings of 2–16 molecules per unit cell. Self-diffusion coefficients were calculated using the Einstein relationship. Hydrogen was found to have higher self-diffusion Coefficients than methane in both the molecular sieve structures under study. However, in the zinc phosphate molecular sieve the methane remained immobile, allowing for purification and separation of hydrogen, whereas in Zeolite A the methane experienced appreciable cage-to-cage motion.     

Recent research on inherent molecular structure,physiochemical properties,and bio-functions of food and feed-type Avena sativa oats and processing-induced changes revealed with molecular microspectroscopic techniques

Avena sativa oat is a cereal widely used as human food and livestock feed. However, the low metabolized energy and the rapid rumen degradations of protein and starch have limited the use of A. sativa oat grains. To overcome this disadvantage, new A. sativa oat varieties have been developed. Additionally, heat-related processing has been performed to decrease the degradation rate and improve the absorption of amino acids in the small intestine. The nutritive value is reflected by both chemical composition and inherent molecular structure conformation. However, the traditional wet chemical analysis is not able to detect the inherent molecular structures within an intact tissue. The advanced synchrotron-radiation and globar-based molecular microspectroscopy have been developed recently and applied to study internal molecular structures and the processing induced structure changes in A. sativa oats and reveal how molecular structure changes in relation to nutrient availability. This review aimed to obtain the recent information regarding physiochemical properties, molecular structures, metabolic characteristics of protein, and the heat-induced changes in new A. sativa oat varieties. The use of the advanced vibrational molecular spectroscopy was emphasized, synchrotron- and globar-based (micro)spectroscopy, to reveal the inherent structure of A. sativa oats at cellular and molecular levels and to reveal the heat processing effect on the degradation characteristics and the protein molecular structure in A. sativa oats. The relationship between nutrient availability and protein molecular inherent structure was also presented. Information described in this review gives better insight in the physiochemical properties, molecular structure, and the heat-induced changes in A. sativa oat detected with advanced molecular spectroscopic techniques in combinination with conventional nutrition study techniques.     

Coherent control of non-resonant two-photon transition in molecular system

In this paper,we study theoretically and experimentally the coherent control of non-resonant two-photon transition in a molecular system (Perylene dissolved in chloroform solution) by shaping the femtosecond pulses with simple phase patterns (cosinusoidal and π phase step-function shape).The control efficiency of the two-photon transition probability is correlated with both the laser field and the molecular absorption bandwidth.Our results demonstrate that,the two-photon transition probability in a molecular system can be reduced but not completely eliminated by manipulating the laser field,and the control efficiency is minimal when the molecular absorption bandwidth is larger than twice the laser spectral bandwidth.     

理论研究激光强度对H2+分子高次谐波产生的影响

本文通过求解非波恩-奥本海默近似条件下的一维含时薛定谔方程来研究脉冲强度对H₂⁺分子高次谐波的影响.由于干涉相消,在啁啾激光场的条件下在谐波谱中出现了干涉最小值.我们用全量子方法计算的时频分布图分析了分子高次谐波产生中的微观机制.此外,数值计算结果显示随着脉冲强度的增加电子的有质动力势随之增加,同时干涉最小值的位置移向谐波的高阶部分.     

Molecular mobility, phase transitions and phase transformations in crystalline ortho- and meta-carboranes

The thermally stimulated depolarisation currents (TSDC) technique was used to study the slow molecular mobility in the crystalline forms of highly symmetric polar isomers of carborane. As a consequence of the high molecular symmetry, that originates a molecular shape with a high degree of globularity, plastic crystalline phases with relatively fast reorientational mobility are expected. The TSDC results showed that there is an orientational glass transformation in phase III of ortho-carborane but not in meta-carborane, reinforcing the conclusions of the calorimetric study that suggests that phase III of m-carborane is an orientationally ordered phase. Furthermore, a slow molecular mobility is detected by TSDC in phase II of o-carborane, some degrees below the II→I transition temperature. The mobility in phase II of m-carborane is too fast to be probed by TSDC. It is suggested that the difference in the dynamic behaviour of the two isomers probably arises from their different polarity.     

Investigation of structure interaction to nutrient properties and utilization in co-products after pellet processing at various conditions using advanced molecular spectroscopy

The molecular infrared (micro)spectroscopy, developed as a rapid, non-destructive and non-invasive analytical technique, is able to reveal structure features at a molecular level and provide tissue structure and chemistry information simultaneously. However, to date, this analytical technique is seldomly used in study processing induced structure change in relation to nutrient properties, utilization, and delivery in livestock. The objective of this article was to review the inter-relationship between molecular structures with nutritive properties and nutrient delivery in co-products from bioenergy production after pelleted processing using vibrational molecular spectroscopy. First, this article reviews recent progress in pelleting process research, related to physical quality of pellets, utilization for animals, processing quality, and current nutrition evaluation methodologies for pelleting. The emphasis of this study focused on the effect of conditioning temperature and time of the pellet processing on molecular structure changes and nutrient properties and nutrient delivery. The methods for nutritive properties and nutrient delivery were reviewed, which included various in vitro, in situ, in vivo, and nutrient modeling techniques. The molecular spectroscopic techniques included globar-sourced and synchrotron-sourced molecular spectroscopic techniques. The molecular spectra analysis included univariate and multivariate molecular spectral analyses. The relationship between molecular structural changes and truly absorbed nutrient supply was quantified. The research provides an insight how inherent structure changes induced by pellet processing on a molecular basis affected nutrient properties, utilization, and availability.     

Orientational order and molecular parameters of two nematogenic mixtures from X-ray studies: confirmation of electro-optical results

This study entails the report of X-ray studies conducted on two nematogenic mixtures (code names ZLI 1221 and ZLI 1291) containing identical moieties: phenyl cyclohexane, biphenyl cyclohexane and cyclohexyl benzoate, but exhibiting different mesogenic ranges and properties. X-ray studies have been undertaken with a view to investigate the difference in the mesogenic behaviour of the said mixtures at the molecular level. The average apparent molecular length ‘l?’ and intermolecular distance ‘D’ of the two mixtures and their variations with temperature have been determined from X-ray data. The orientational order parameters ?P ₂? and ?P ₄? and their thermal variations have also been obtained. Comparison has been made with the ?P ₂? values obtained from X-ray study with those obtained from optical study. The average apparent molecular lengths of the two mixtures corroborate the findings regarding the relative molecular weights of the two samples obtained from optical and dielectric data.     

Conformational polymorphism of the antidiabetic drug chlorpropamide

In this paper, the main features of Raman spectroscopy, one of the first choice methods in the study of polymorphism in pharmaceuticals, are presented taking chlorpropamide as a case of study. The antidiabetic drug chlorpropamide (1‐[4‐chlorobenzenesulphonyl]‐3‐propyl urea), which belongs to the sulfonylurea class, is known to exhibit, at least, six polymorphic phases. These forms are characterized not only by variations in their molecular packing but also in their molecular conformation. In this study, the polymorphism of chlorpropamide is discussed on the basis of Raman scattering measurements and quantum mechanical calculations. The main spectroscopic features that fingerprint the crystalline forms are correlated with the corresponding crystalline structures. Using a theoretical approach on the energy dependence of the conformers, simulated molecular torsion angles are plotted versus the formation energy, which provides a satisfactory agreement between the torsion angles at the energy minima and the experimental values observed in the different solid forms of chlorpropamide. Copyright © 2011 John Wiley & Sons, Ltd.     

Collisions of ultracold trapped cesium Feshbach molecules

We study collisions in an optically trapped, pure sample of ultracold Cs₂ molecules in various internal states. The molecular gas is created by Feshbach association from a near-degenerate atomic gas, with adjustable temperatures in the nanokelvin range. We identify several narrow loss resonances, which point to the coupling to more complex molecular states and may be interpreted as Feshbach resonances in dimerdimer interactions. Moreover, in some molecular states we observe a surprising temperature dependence in collisional loss. This shows that the situation cannot be understood in terms of the usual simple threshold behavior for inelastic two-body collisions. We interpret this observation as further evidence for a more complex molecular structure beyond the well-understood dimer physics.     

Structure and energetics of molecular point defects in ice Ih

We present a first-principles study of the molecular vacancy and three distinct molecular interstitial structures in ice Ih. The results indicate that, due to its bonding to the surrounding hydrogen-bond network, the bond-center (Bc) configuration is the favored molecular interstitial in ice Ih. A comparison between the vacancy and the Bc interstitial suggests that the former is the predominant molecular point defect for T approximately < 200K although a crossover scenario in which the latter becomes favored below the melting point is conceivable.     

基于表面等离激元场的分子反射镜的理论研究

本文提出了一种基于微纳金属膜结构激发的表面等离激元场的分子反射镜新方案,利用中性分子与金属表面垂直方向上蓝失谐消逝波光场之间的偶极力相互作用,实现入射分子束的表面反射.理论计算了表面等离激元场的空间分布,用蒙特卡洛方法模拟了分子在该场中运动的动力学过程,得到了分子反射镜的反射率与相互作用时间和入射光强之间的关系.结果表明:当入射激光脉宽为10 ns,光强为I=1.0×109W/cm2时,纵向温度为10 mK,横向温度为1 mK的碘分子束反射效率达到55.89%,而且反射率随着入射光强的增大而增大.     

利用HIRFL-CSR开展分子离子复合离解研究的可行性分析

介绍了储存环高精度分子谱学研究的科学意义、 国内外研究现状和利用HIRFL-CSR开展该项研究的优势, 着重论证了HIRFL-CSR分子离子注入实验环的总体设计方案和技术方案。 通过在HIRFL-CSR实验环上增建一条分子离子注入线, 将实验环改造成能兼顾现有物理实验和大分子物理研究的综合性研究平台, 为分子离子复合离解研究提供良好的技术支撑。 特别是质量数大于70的分子离子, 能显著提高其能量分辨。 In the present paper, it is introduced the scientific background and the current status of the high precision spectroscopy of the molecular ions at cooler storage ring. The advantages to study the dissociative recombination(DR) processes using cooler storage ring CSRe are discussed. The physics design,the main parameters of the injection beam line and the injection of the molecular ions into the CSRe and the key techniques are described in detail. With a new injection beam line,HIRFL-CSRe will be reconstructed to a multi discipline research platform,offering good opportunities for the study of DR processes of molecular ions,especially for that of the molecular ions of m>70 amu with much improved resolution.     

Strain-induced reorientation and mobility in nematic liquid-crystalline elastomers as studied by time-resolved FTIR spectroscopy

Polarized Fourier transform infrared (FTIR) spectroscopy is employed to study the segmental orientation and mobility of liquid-crystalline elastomers (LCEs) with a monodomain structure in response to external mechanical fields parallel and perpendicular to the initial nematic director. The mean orientation and the molecular order parameter of the different molecular moieties referring to the mesogen, the spacer and the network are analyzed in detail. Parallel stretch leaves the mean orientation of the different molecular moieties and its molecular order parameter nearly uninfluenced. Perpendicular stretch results in a threshold-like dependence: for elongation ratios λ ⩽ λ_c = 1.3 (10 mol% crosslinker density), respectively λ ⩽ λ_c = 1.6 (5 mol% crosslinker density) no change of the mean orientation and the molecular order parameters is observed, while for λ ≥ λ_c all molecular units reorient and their molecular order parameters are strongly decreased. The present studies give no indications that the reorientational dynamics of the network and the mesogens differ as long as the elongation ratio is smaller than λ_c.     

Possibilities for controlling attosecond x-ray pulse generation during molecular ionization by femtosecond laser radiation

We discuss the role of different factors (molecular sizes and configuration, orientation of the molecular axis with respect to the electric field of a laser pulse, the type of the molecular orbital, etc.), which characterize molecules and their state, in the formation of the nonlinear response of a molecule ionized by a high-power femtosecond laser pulse. In numerical experiments within the framework of a two-dimensional model for the H ₂ ⁺ molecular ion, we study possibilities for controlling the process of nonlinear frequency conversion of femtosecond optical radiation into X-ray radiation of attosecond duration by means of preliminary vibrational or electronic excitation of molecules. We demonstrate the possibilities of using the attosecond pulse generation as a diagnostic tool for probing vibration-rotational dynamics of molecules.     

Surface dynamics studied by time-dependent tunneling current

Scanning tunneling microscopy (STM) is not only an excellent tool for the study of static geometric structures and electronic structures of surfaces due to its high spatial and energy resolution, but also a powerful tool for the study of surface dynamic behaviors, including surface diffusion, molecular rotation, and surface chemical reactions. Because of the limitation of the scanning speed, the video-STM technique cannot study the fast dynamic processes. Alternatively, a time-dependent tunneling current, I-t curve, method is employed in the research of fast dynamic processes. Usually, this method can detect about 1000 times faster dynamic processes than the traditional video-STM method. When placing the STM tip over a certain interesting position on the sample surface, the changing of tunneling current induced by the surface dynamic phenomena can be recorded as a function of time. In this article, we review the applications of the time-dependent tunneling current method to the studies of surface dynamic phenomena in recent years, especially on surface diffusion, molecular rotation, molecular switching, and chemical reaction.     

Ab initio molecular dynamics of liquid carbon disulphide

An ab initio molecular dynamics study has been made of molecular liquid CS₂ using a density functional approach in the quasi-local ‘generalized gradient approach’ (GGA). Various aspects of the liquid at a microscopic level have been investigated including dynamic effects on structure such as velocity autocorrelation functions, vibrational modes and position and angular correlation functions. Results are presented on the molecular electronic structure at finite temperature, including the fluctuating molecular dipole moment and its relationship to atomic position and normal modes. Although the GGA is explicitly incapable of describing non-local exchange-correlation effects which are conventionally believed to be important in this system, these results are nevertheless in good agreement with experiment.     

Single molecular shuttle-junction: Shot noise and decoherence

Single molecular shuttle-junction is one kind of nanoscale electromechanical tunneling system. In this junction, a molecular island oscillates depending on its charge occupation, and this charge dependent oscillation leads to modulation of electron tunneling through the molecular island. This paper reviews recent development on the study of current, shot noise and decoherence of electrons in the single molecular shuttle-junction. We will give detailed discussion on this topic using the typical system model, the theory of fully quantum master equation and the Aharonov–Bohm interferometer.     

Theoretical and vibrational spectroscopic studies on binary mixture of o‐chlorobenzaldehyde

In this work, a combined theoretical and spectroscopic study of binary mixture of liquid o‐chlorobenzaldehyde (OCBZ) is reported using ab initio calculations, Raman and infrared (IR) spectroscopies. The purpose of this study was twofold: firstly, to describe the interaction of OCBZ in terms of bonding energies and preferred geometries; secondly, to characterize the spectroscopic effects on the vibrational modes of OCBZ in the binary mixture of different polar and nonpolar solvents. Ab initio calculations have proven to be a valuable tool for predicting relevant molecular structure and molecular parameters in the intermolecular interactions. Copyright © 2008 John Wiley & Sons, Ltd.     

New Approaches and Recent Advances on Characterization of Chemical Functional Groups and Structures,Physiochemical Property,and Nutritional Values in Feedstocks and By-Products: Advanced Spectroanalytical and Modeling Investigations

Abstract: Molecular spectroscopy technique, a rapid and noninvasive analytical technique, is able to reveal biomaterials’ structural features. However, to date, this technique is seldom used in the biofuel and bioethanol processing industry. This article aims to provide research progress and updates on molecular spectroscopy of feedstocks and coproducts from biofuel/bioethanol processing and to show how to use this molecular technique to study the molecular structure, chemical functional groups, and physiochemical properties of feedstocks and coproducts from biofuel processing and how structural changes affect nutrient availability.     

High-resolution spectroscopy on trapped molecular ions in rotating electric fields: A new approach for measuring the electron electric dipole moment

High-resolution molecular spectroscopy is a sensitive probe for violations of fundamental symmetries. Symmetry violation searches often require, or are enhanced by, the application of an electric field to the system under investigation. This typically precludes the study of molecular ions due to their inherent acceleration under these conditions. Circumventing this problem would be of great benefit to the high-resolution molecular spectroscopy community since ions allow for simple trapping and long interrogation times, two desirable qualities for precision measurements. Our proposed solution is to apply an electric field that rotates at radio frequencies. We discuss considerations for experimental design as well as challenges in performing precision spectroscopic measurements in rapidly time-varying electric fields. Ongoing molecular spectroscopy work that could benefit from our approach is summarized. In particular, we detail how spectroscopy on a trapped diatomic molecular ion with a ground or metastable ³Δ₁ level could prove to be a sensitive probe for a permanent electron electric dipole moment (eEDM).