PuH2气态分子热力学稳定性的理论研究

用密度泛函B3LYP方法计算了PuH2分子的微观性质、不同温度下气态PuH2分子的能量（E）、熵（S）及气态PuH2分子生成反应的标准焓变ΔH、标准熵变ΔS和标准自由能变ΔG.计算结果表明，气态PuH2分子不具有热力学稳定性.     

Thermodynamic analysis of uranium oxides fluorination with HF(g) and F2(g)

Journal of Radioanalytical and Nuclear Chemistry - Implementation of a state of the art data acquisition and analysis program for variable low energy positron beam using LabVIEW based automation...     

Thermodynamic interpretation of the scaling of the dynamics of supercooled liquids

The recently discovered scaling law for the relaxation times, tau(T,upsilon) = I(Tupsilon(gamma)), where T is temperature and upsilon the specific volume, is derived by a revision of the entropy model of the glass transition dynamics originally proposed by Avramov [J. Non-Cryst. Solids 262, 258 (2000)]. In this modification the entropy is calculated by an alternative route. The resulting expression for the variation of the relaxation time with T and upsilon is shown to accurately fit experimental data for several glass-forming liquids and polymers over an extended range encompassing the dynamic crossover. From this analysis, which is valid for any model in which the relaxation time is a function of the entropy, we find that the scaling exponent gamma can be identified with the Gruneisen constant.     

PuC2 气态分子的结构与热力学稳定性研究

在相对论有效原子实势近似下,用密度泛函B3LYP方法,求得PuC2气态分子的结构与不同温度下的热力学函数.根据热力学原理,计算得到PuC2气态分子在不同温度下的标准生成自由能变均为较大正值,据此说明, PuC2气态分子不具有热力学稳定性.     

Molecular dynamics in thin (grafted) polymer layers

Broadband dielectric spectroscopy is employed to study the molecular dynamics in thin polymer layers of (spin-coated) cis-1, 4-polyisoprene (PI) and of (grafted and spin-coated) polydimethylsiloxane (PDMS). For the former, besides the segmental and the normal mode relaxation, a confinement-induced mode is observed, which is assigned to fluctuations of terminal subchains. It turns out that the uptake of water has a strong influence on the dynamics of this relaxation, which takes place in the immediate vicinity of the interface. Between grafted and spin-coated PDMS a pronounced difference in the dynamics is observed for layers that are comparable in thickness to the radius of gyration of the confined chain. This is attributed to the different conformation of grafted and spin-coated polymer layers.     

Thermodynamic characterization of interpenetrating polymer networks of poly (carbonate-urethane) and poly (methyl methacrylate)

Crosslinked poly (methyl methacrylate) and poly (carbonate-urethane) as well as full interpenetrating network on their base (IPN) were characterized by precise heat capacity measurements in the temperature interval 1.2–150 K. As judged by the positive sign of the excess Gibbs free energy in the whole temperature interval above 30 K, the apparently single-phase state of IPN is thermodynamically unstable; however, its kinetic stability is ensured by permanent chamical crosslinks prohibiting the incipient phase separation. © 1994 John Wiley & Sons, Inc.     

Thermodynamic scaling of diffusion in supercooled Lennard-Jones liquids

The manner in which the intermolecular potential u(r) governs structural relaxation in liquids is a long standing problem in condensed matter physics. Herein, we show, in agreement with recent experimental results, that diffusion coefficients for simulated Lennard-Jones m-6 liquids (8 < or = m < or = 36) in normal and moderately supercooled states are a unique function of the variable rhogamma/T, where rho is density and T is temperature. The scaling exponent gamma is a material specific constant whose magnitude is related to the steepness of the repulsive part of u(r), evaluated around the distance of closest approach between particles probed in the supercooled regime. Approximations of u(r) in terms of inverse power laws are also discussed.     

Kinetic versus Thermodynamic Control Over Multiple Conformations of Di-2,7-naphthihexaphyrin(1.1.1.1.1.1)

Di-2,7-naphthihexaphyrin(1.1.1.1.1.1), a non-aromatic carba-analogue of the hexaphyrin(1.1.1.1.1.1), incorporating two built-in 2,7-naphthylene moieties was synthesized as two separate, conformationally locked stereoisomers. Both conformers followed complex protonation pathways involving structurally different species, which can be targeted under kinetic and thermodynamic control. The neutralization of the ultimate dicationic product, accessible from both stereoisomers of the free base, allowed to realize the complex conformational switching cycle involving six structurally different species.     

Competitive spreading versus imbibition of polymer liquid drops in nanoporous membranes: scaling behavior with viscosity

The way a liquid drop that is in contact with a nanoporous substrate evolves essentially depends on the competition between imbibition and spreading. Although the scaling behavior of this competitive process with liquid viscosity is important for various applications requiring the filling of nanoporous substrates (template-assisted fabrication, storage, and controlled release of liquids), they appear to be poorly investigated and insufficiently understood. We developed a model study to investigate the wetting and spontaneous imbibition of silicon oil drops of viscosities ranging from 1 to 100 Pa s on nanoporous alumina membranes (pore size of 200 nm). Our results show that the drop radius essentially follows the power law t1/10 time dependence as expected by Tanner's law. However, the scaling of the spreading velocity with the viscosity (approximately eta-n) was found to display an exponent that is comparable on both the reference (impermeable) and nanoporous substrates (n = 0.55) but notably higher than theoretically expected (0.1). More surprisingly, we show that despite the confinement, the rate of imbibition into the nanopores displays a weaker dependence on the viscosity, as compared to the spreading velocity on both the reference and nanoporous substrates. On the basis of Darcy's law for capillary-driven imbibition, this result was discussed in the context of the scaling behavior of the contact angle with the viscosity.     

Isomerism and thermodynamics of the HF(g) and HCl(g) association

The thermodynamics of the association of HF(g) and HCl(g) leading to formation of two isomeric complexes HF· HC1 and HC· HF have been studied. This computational study makes use of the molecular parameters from quantum-chemical calculations. The evaluation of the thermodynamics has been carried out for full harmonic vibrational partition function and, simultaneously, for treating torsional vibration as free internal rotation. The characterisation of the latter motion is connected with a study of the effect of choice of the free internal-rotational axis. Attention is also paid to the interplay of both isomeric structures which are present at comparable concentrations at modest and higher temperatures even though the HF · HC1 structure is relatively more populated.     

The isomolecular exchange reaction Ga2S(g) + In2S(g) = 2 InGaS(g)

Equilibria involving the molecules Ga₂S(g), In₂S(g), and InGaS(g), by the reaction Ga₂S(g) + In₂S(g) = 12InGaS(g) were investigated between 1060–1350 K by the Knudsen-effusion, mass-spectrometric method. The reaction enthalpy at 298 K was calculated to be 0±1 kJ mol⁻¹. The enthalpy of formation of InGaS at 298 K and the enthalpy of atomization of InGaS at 298 K were calculated to be 80±18 kJ mol⁻¹ and 710±18 kJ mol⁻¹, respectively. The equilibrium constant and the enthalpy of reaction indicated that the three gaseous molecules have a bent triatomic structure in which S is a center atom and no bond between metals.     

Dynamic scaling of polymer gels comprising nanoparticles

We present dynamic light scattering (DLS) measurements of soft poly(methyl-methacrylate) (PMMA) and polyacrylamide (PA) polymer gels prepared with trapped bodies (latex spheres or magnetic nanoparticles). We show that the anomalous diffusivity of the trapped particles can be analyzed in terms of a fractal Gaussian network gel model for the entire time range probed by DLS technique. This model is a generalization of the Rouse model for linear chains extended for structures with power law network connectivity scaling, which includes both percolating and uniform bulk gel limits. For a dilute dispersion of strongly scattering particles trapped in a gel, the scattered electric field correlation function at small wavevector ideally probes self-diffusion of gel portions imprisoning the particles. Our results show that the time-dependent diffusion coefficients calculated from the correlation functions change from a free diffusion regime at short times to an anomalous subdiffusive regime at long times (increasingly arrested displacement). The characteristic time of transition between these regimes depends on scattering vector as approximately q(-2), while the time decay power exponent tends to the value expected for a bulk network at small q. The diffusion curves for all scattering vectors and all samples were scaled to a single master curve.     

Hyperfine structures of the 2 (3)Sigma(g) (+), 3 (3)Sigma(g) (+), and 4 (3)Sigma(g) (+) states of Na(2)

The hyperfine structures of the 2 (3)Sigma(g) (+), 3 (3)Sigma(g) (+), and 4 (3)Sigma(g) (+) states of Na(2) have been resolved with sub-Doppler continuous wave perturbation facilitated optical-optical double resonance spectroscopy via A (1)Sigma(u) (+) approximately b (3)Pi(u) mixed intermediate levels. The hyperfine patterns of these three states are similar. The hyperfine splittings of the low rotational levels are all very close to the case b(betaS) limit. As the rotational quantum number increases, the hyperfine splittings become more complicated and the coupling cases become intermediate between cases b(betaS) and b(beta J) due to spin-rotation interaction. We present a detailed analysis of the hyperfine structures of these three (3)Sigma(g) (+) states, employing both case b(betaS) and b(beta J) coupling basis sets. The results show that the hyperfine splittings of the (3)Sigma(g) (+) states are mainly due to the Fermi-contact interaction. The Fermi contact constants for the two d sigma Rydberg states, the 2 (3)Sigma(g) (+) and 4 (3)Sigma(g) (+), are 245+/-5 MHz and 225+/-5 MHz, respectively, while the Fermi contact constant of the s sigma 3 (3)Sigma(g) (+) Rydberg state is 210+/-5 MHz. The diagonal spin-spin and spin-rotation constants, and nuclear spin-electronic spin dipolar interaction parameters of the 3 (3)Sigma(g) (+) and 4 (3)Sigma(g) (+) states are also obtained.     

Photooxidation of Tryptophan: O2(1Δg) versus Electron-Transfer Pathway

Abstract— Tris (2,2'-bipyridyl)ruthenium(II)chloride hexahydrate (Ru[bpy]₃²+) free in solution and adsorbed onto antimony-doped SnO₂ colloidal particles was used as a photosensitizer for a comparison of the O₂(¹Δ_g) and electron-transfer-mediated photooxidation of tryptophan (TRP), respectively. Quenching of excited Ru(bpy)₃²+ by O₂(³σ_g^?) in an aerated aqueous solution leads only to the formation of O₂(¹Δ_g) (φ₄= 0.18) and this compound was used as a type II photosensitizer. Excitation of Ru(bpy)₃²+ adsorbed onto Sb/SnO₂ results in a fast injection of an electron into the conduction band of the semiconductor and accordingly to the formation of Ru(bpy)₃²+ and was used for the sensitization of the electron-transfer-mediated photooxidation. The Ru(bpy)₃³+ is reduced by TRP with a bimolecular rate constant k_Q= 5.9 × 10⁸M^?1 s^?1, while O₂(¹Δ_g) is quenched by TRP with k_t= 7.1 × 10⁷M^?1 s^?1 (chemical + physical quenching). Relative rate constants for the photooxidation of TRP (k_c) via both pathways were determined using fluorescence emission spectroscopy. With N_p, the rate of photons absorbed, being constant for both pathways we obtained k_c= (372/N_p) M^?1 s^?1 for the O₂(¹Δ_g) pathway and k_c≥ (25013/N_p) M^?1 s^?1 for the electron-transfer pathway, respectively. Thus the photooxidation of Trp is more than two orders of magnitude more efficient when it is initiated by electron transfer than when initiated by O₂(¹Δ_g).     

Experimentelle Bestimmung und Voraussage der Dissoziationsenthalpien von AuDY(g) und AgDy(g)

Ohne Zusammenfassung     

Experimentelle Bestimmung und Voraussage der Dissoziationsenthalpien von AuDY(g) und AgDy(g)

Ohne Zusammenfassung     

Thermodynamic properties of some concentrated polymer solutions

Solubilities of several solvents were measured in four molten polymers by using an isobaric vapor-pressure apparatus. Solvent concentration ranged from 0.5 to 15 wt-%. The systems polyisoprene–benzene and polyisobutylene–benzene were studied at 80.0°C; polyisobutylene–cyclohexane was studied at 100.0°C; ethylene–vinyl acetate copolymer (EVA)–cyclohexane, EVA–isooctane, and poly(vinyl acetate)–isooctane were studied at 110.0°C. Of six polymer–solvent systems studied, all except poly(vinyl acetate)–isooctane appear to exhibit hysteresis in a single sorption–desorption cycle starting with dry polymer. The desorption curves of solvent activity plotted versus solvent weight fraction show an inflection point, suggesting localized adsorption of solvent molecules. Experimental data were analyzed with a theory which takes into account adsorption of solvent by polymer in addition to differences in free volumes and intermolecular forces. The theory gives a semiquantitative representation of the experimental data.     

Ion conduction and polymer dynamics of poly(2-vinylpyridine)-lithium perchlorate mixtures

Ion conduction and polymer dynamics of homogeneous mixtures of poly(2-vinylpyridine) (P2VPy) with 0.1 to 10 mol % lithium perchlorate (LiClO(4)) were investigated using broadband dielectric spectroscopy. Interpretation of the relaxation behavior was assisted by findings from differential scanning calorimetry, Fourier transform infrared spectroscopy, dynamic mechanical analysis, and wide-angle and small-angle X-ray scattering experiments. Five dielectric relaxations were observed: a local beta-process in the glassy state, a segmental relaxation, a slow segmental process, an ion-mode relaxation, and electrode polarization. The local P2VPy beta-relaxation was strongly suppressed with increasing LiClO(4) content arising from the formation of transient crosslinks, which lead to a subsequent decrease in the number of free pyridine groups and/or a reduction in the local free volume in the presence of LiClO(4). Ion conduction at low LiClO(4) concentrations (<10 mol %) is governed by the diffusion of anions through the matrix, which is strongly coupled with the segmental relaxation. At relatively high LiClO(4) concentration (10 mol %), partial decoupling between ion motion and the segmental relaxation was observed, leading to increased conductivity.     

On the density scaling of liquid dynamics

Superpositioning of relaxation data as a function of the product variable TV(γ), where T is temperature, V the specific volume, and γ a material constant, is an experimental fact demonstrated for approximately 100 liquids and polymers. Such scaling behavior would result from the intermolecular potential having the form of an inverse power law (IPL), suggesting that an IPL is a good approximation for certain relaxation properties over the relevant range of intermolecular distances. However, the derivation of the scaling property of an IPL liquid is based on reduced quantities, for example, the reduced relaxation time equal to T(1∕2V - 1∕3) times the actual relaxation time. The difference between scaling using reduced rather than unreduced units is negligible in the supercooled regime; however, at higher temperature the difference can be substantial, accounting for the purported breakdown of the scaling and giving rise to different values of the scaling exponent. Only the γ obtained using reduced quantities can be sensibly related to the intermolecular potential.