高温高压下稠密氢的离解与电离

应用自恰变分自由能模型描述了在化学平衡下,H2,H,H ,e构成地混合物在天体物理和高压实验中遇到情形下的各种相互作用及压力与温度效应引起地离解和电离现象.目前的模型预测了在压力电离区存在一热力学不稳定状态,当温度Tc=15.5 kK,压力Pc=58.3 GPa和密度ρc=0.3226 g/cm3时发生等离子体相变,此理论预测结果与各种模型计算结果进行了比较分析.     

Triplet excitations at high temperatures in 1:1 TCNQ-salts

High temperature properties of triplet excitations in TCNQ-salts are theoretically studied. Formulas for the energy and concentration of triplet excitons as functions of temperature are obtained. The static magnetic susceptibility of triplet excitons is calculated. A possible appearance of short range order in the excitation density is discussed. A high-concentration modification of the molecular exciton theory is used throughout the paper.I would like to express thanks to Dr. W.Siebrand of N.R.C., Ottawa, for introducing me into problems in charge-transfer crystals. I also thank Professor M.Trlifaj for interesting discussions.     

Pressure-induced molecular dissociation in iodine at low temperatures

Abstract

Synchrotron x-ray diffraction experiments at low temperatures have revealed that even at 35K the molecular dissociation starts taking place at P_S=21.5 and finishes at P_f=26.1GPa. An extrapolation of the phase boundary thus obtained at several temperatures intersects the T=4K line at P_S=21.6 and P_f=26.3GPa. This result, inferring the monatomic structure to be realized at P=30GPa and T=4K, leads to a discrepancy against the recent Mössbauer result obtained at the same point in the P-T phase diagram.     

Diffusive transport in spin-1 chains at high temperatures

We present a numerical study on the spin and thermal conductivities of the spin-1 Heisenberg chain in the high temperature limit, in particular, the Drude weight contribution and frequency dependence. We use the exact diagonalization and the recently developed microcanonical Lanczos method; it allows us a finite size scaling analysis by the study of significantly larger lattices. This work, pointing to a diffusive rather than ballistic behavior, is discussed with respect to other recent theoretical and experimental studies.     

Subthreshold sputtering at high temperatures

The sputtering of tungsten from a target at a temperature of 1470 K during irradiation by 5-eV deuterium ions in a steady-state dense plasma is discovered. The literature values of the threshold for the sputtering of tungsten by deuterium ions are 160–200 eV. The tungsten sputtering coefficient measured by the loss of weight is found to be 1.5×10^?4 atom/ion at a deuterium ion energy of 5 eV. Previously, such a sputtering coefficient was usually observed at energies of 250 eV. The sputtering is accompanied by a change in the target surface relief, i.e., by the etching of the grain boundaries and the formation of a wavy structure on the tungsten surface. The subthreshold sputtering at a high temperature is explained by the possible sputtering of adsorbed tungsten atoms that are released from the traps around the interstitial atoms and come to the target surface from the space between the grains. The wavy structure on the surface results from the merging of adsorbed atoms into ordered clusters.     

3d-Magnets at high temperatures

Recent achievements in solving the problem of the microscopic nature of the ferromagnetic-to paramagnetic-phase transition of ferromagnetic metals by employing the method of spin- and angle-resolved photoemission spectroscopy with synchrotron radiation (from the storage ring BESSY in Berlin) are briefly summarized. Emphasize is also given to the theoretical interpretation of the data, from which a short-range order in Fe near the Curie pointT _c of at least 4 Å has been derived. This excludes the validity of the disordered local moment picture for Fe at high temperatures.     

MAS-NMR at very high temperatures

We report MAS-NMR experiments at temperatures of approx. 1200 K using a CO(2) laser as the heating device. An internal NMR thermometer based on the (7)Li T1 data of Li(0.24)La(0.54)TiO(3) is used for temperature calibration. Using this setup, temperatures as high as 1191 K could be reached under MAS conditions as confirmed by the melting of Li(2)B(4)O(7) at 1191 K which could be followed by (7)Li-MAS-NMR.     

Diffractive dissociation on deuterons at high energies

It is shown that a study of the screening effect in the reaction p + d → X + d may yield important information about the space-time picture of high-energy hadron scattering. Arguments are given in support of the suggestion that in the parton picture of strong interactions the rescattering term in diffractive dissociation should be as large as in elastic scattering. The experimental data on the reaction p + d → X + d at energies higher than 100 GeV are analysed.     

Heavy quarkonia properties at high temperatures

The spectra and e ⁺ e ⁻ decay widths of the heavy quarkonia as a function of the temperature of medium generated in the ultrarelativistic heavy-ion collisions are discussed. The fluctuations of the vacuum gluon fields are estimated within the instanton liquid model approach. It is noticed that the parameters that are considered can be used to indicate the gluon warming.     

Multiphoton dissociation of diatomic molecules at high intensities

A non-perturbative method is used to obtain an analytic expression for the rate of multiphoton dissociation of diatomic molecules as a function of the incident radiation. The two-photon dissociation process is considered as an example.     

Structure changes in vacancy-rich titanium monoxide at high pressures and high temperatures

Abstract

Powdered samples of TiO_0.82, TiO_1.04 and TiO_1.25 having the cubic rocksalt-type structure with high concentration of vacancies randomly distributed were held at combined conditions of high pressure, ranging from 1 GPa to 8 GPa, and high temperature, ranging from 973 K to 1173 K, and structural changes occurring were investigated by synchrotron radiation diffraction at the conditions and by conventional X-ray diffraction after the samples were brought back to ambient condition. Pressure has been shown to suppress formation of ordered arrangements of vacancies in all the samples and lead to precipitation of a hexagonal δ-Ti₃O₂ in TiO_0.82 and TiO_1.04 and precipitation of a corundum-type Ti₂O₃ in TiO_1.25. Irreversible change in the lattice parameter of the remaining rocksalt-type structure has been observed which is due to partial annihilation of vacancies under pressure.     

Dissociation of dimethyl ether at high temperatures

The decomposition of dimethyl ether (CH₃OCH₃) has been investigated behind incident shock waves in a diaphragmless shock tube using laser schlieren densitometry, LS (T = 1500–2450 K, P = 57 ± 4, 125 ± 5 and 253 ± 12 Torr). The LS density gradient profiles were simulated and excellent agreement was found between the simulations and experimental profiles. Rate coefficients for CH₃OCH₃ → CH₃O + CH₃ were obtained. They showed strong fall-off, and at the lower end of the experimental temperature range are close to the low pressure limit. First order rate coefficient expressions were determined over 1500 < T < 2450 K. k_57Torr = (3.10 ± 1.0) × 10⁷⁹T^?19.03 exp(?54417/T) s^?1, k_125Torr = (1.12 ± 0.3) × 10⁸³T^?19.94 exp(?55554/T) s^?1and k_253Torr = (1.02 ± 0.3) × 10⁷³T^?17.09 exp(?51500/T) s^?1. The effect of a roaming channel for decomposition of dimethyl ether was assessed and the best agreement was obtained with 1% dissociation of DME via the roaming path.     

Phonon linewidths of NaF at high temperatures

The linewidths of transverse acoustic modes in NaF are calculated for temperatures up to the melting point. We show that the widths decrease in a certain long wavelength region with increasing temperatures. The results are compared with recent neutron experiments up to 700 K.     

Density of indium antimonide at high temperatures

The density of solid and liquid indium antimonide was studied by irradiating the samples with a narrow beam of monochromatic gamma-radiation in the temperature range of 293–1950 K, including the range of melting — crystallization. The measurement errors for the density and thermal expansion coefficients were ±(0.25–0.40) % and ± 4 %, correspondingly. The approximating equations and tables of reference data were obtained for the temperature dependence of thermal properties. Measurement results were compared with the known published data. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 06-08-00040).