Theoretical study on the interaction of heptafluoro-iso-butyronitrile decomposition products with Al (1 1 1)

Seeking environmentally friendly gas-insulated medium has become a research hotspot in recent years. At present, C₃F₇CN (Heptafluoro-iso-butyronitrile) is considered to be a potential SF₆ environment-friendly alternative gas and some achievements have been made in the study of its insulation and decomposition characteristics, but there are few reports on the compatibility between its characteristic decomposition products and materials. The investigation of compatibility between gas-insulated medium and material is an important part of evaluating its comprehensive performance. In this paper, we investigated the interaction between C₂F₅CN, CF₃CN, COF₂ and CF₄ with the aluminium widely used in electrical equipment. It was found that the interaction between C₂F₅CN, CF₃CN and Al (1 1 1) surface is strong. There are obvious charge transfer and electron orbital overlap between the C atom, N atom in CN group and Al (1 1 1). The interaction between COF₂, CF₄ and Al (1 1 1) surface is weak and van der Waal’s forces play the major role. Relevant results reveal the characteristics of C₃F₇CN decomposition products and provide theoretical guidance for evaluating the material compatibility between C₃F₇CN decomposition products and aluminium.     

Applications of DNP-NMR for the measurement of heteronuclear T1 relaxation times

Measurement of heteronuclear spin-lattice relaxation times is hampered by both low natural abundance and low detection sensitivity. Combined with typically long relaxation times, this results in extended acquisition times which often renders the experiment impractical. Recently a variant of dynamic nuclear polarisation has been demonstrated in which enhanced nuclear spin polarisation, generated in the cryo-solid state, is transferred to the liquid state for detection. Combining this approach with small flip angle pulse trains, similar to the FLASH-T(1) imaging sequence, allows the rapid determination of spin-lattice relaxation times. In this paper we explore this method and its application to the measurement of T(1) for both carbon-13 and nitrogen-15 at natural abundance. The effects of RF inhomogeneity and the influence of proton decoupling in the context of this experiment are also investigated.     

T1 measurements incorporating flip angle calibration and correction in vivo

In this work, we propose a variable FA method that combines in vivo flip angle (FA) calibration and correction with a short TR variable FA approach for a fast and accurate T(1) mapping. The precision T(1)s measured across a uniform milk phantom is estimated to be 2.65% using the conventional (slow) inversion recovery (IR) method and 28.5% for the variable FA method without FA correction, and 2.2% when FA correction is included. These results demonstrate that the sensitivity of the variable FA method to RF nonuniformities can be dramatically reduced when these nonuniformities are directly measured and corrected. The acquisition time for this approach decreases to 10 min from 85 min for the conventional IR method. In addition, we report that the averaged T(1)s measured from five normal subjects are 900 +/- 3 ms, 1337 +/- 8 ms and 2180 +/- 25 ms in white matter (WM), gray matter (GM) and cerebral spinal fluid (CSF) using the variable flip angle method with FA correction at 3 T, respectively. These results are consistent with previously reported values obtained with much longer acquisition times. The method reduces the total scan time for whole brain T(1) mapping, including FA measurement and calibration, to approximately 6 min. The novelty of this method lies in the in vivo calibration and the correction of the FAs, thereby allowing a rapid and accurate T(1) mapping at high field for many applications.     

FTIR spectroscopy and estimation of the global warming potential of CF3Br and C2F4

High-resolution (0.03 cm⁻¹) absolute infrared photoabsorption cross sections of bromotrifluoromethane (CF₃Br) and tetrafluoroethylene (C₂F₄) have been measured using Fourier-transformed infrared (FTIR) spectroscopy at temperatures between 213 and 296 K. The measured cross sections were subsequently used to estimate the radiative forcings and the global warming potentials of these two species.     

Measuring nanopore size from the spin-lattice relaxation of CF4 gas

The NMR 19F spin-lattice relaxation time constant T1 for CF4 gas is dominated by spin-rotation interaction, which is mediated by the molecular collision frequency. When confined to pores of approximately the same size or smaller than the bulk gas mean free path, additional collisions of molecules with the pore walls should substantially change T1. To develop a method for measuring the surface/volume ratio S/V by measuring how T1 changes with confinement, we prepared samples of known S/V from fumed silica of known mass-specific surface area and compressed to varying degrees into cylinders of known volume. We then measured T1 for CF4 in these samples at varying pressures, and developed mathematical models for the change in T1 to fit the data. Even though CF4 has a critical temperature below room temperature, we found that its density in pores was greater than that of the bulk gas and that it was necessary to take this absorption into account. We modeled adsorption in two ways, by assuming that the gas condenses on the pore walls, and by assuming that gas in a region near the wall is denser than the bulk gas because of a simplified attractive potential. Both models suggested the same two-parameter formula, to which we added a third parameter to successfully fit the data and thus achieved a rapid, precise way to measure S/V from the increase in T1 due to confinement in pores.     

Fluorocarbon plasmas for nanotexturing of polymers: A route to water-repellent antireflective surfaces

In this work the roughening of polystyrene by means of radiofrequency plasmas fed with CF₄ has been studied. The effect of the Ar addition to the feed, the input power and the treatment duration has been investigated in terms of etching and fluorination degree. Wettability and reflectance performances of selected textured surfaces, coated with a fluorocarbon film from a C₄F₈ fed plasma, have been characterized. All the considered surfaces, even those poorly structured, once coated, show slippery superhydrophobicity, while antireflective transparency appears to be limited to precise texturing characteristics.     

Thermal infrared cross-sections of C2F6 at atmospheric temperatures

Spectral absorption cross-sections, k_ν (), have been measured in the 8.0 and bands of C₂F₆. Temperature and total (N₂-broadening) pressure have been varied to represent the conditions specified in various models of the terrestrial atmosphere so that the absorption cross-sections can be applied directly to the optical remote-sensing of C₂F₆ in the atmosphere. The measured absolute intensities of the 8.0 and the bands are (1.636±0.003)×10⁻¹⁶ and (, respectively.     

Numerical simulation on the influence of water spray in thermal plasma treatment of CF4 gas

Nitrogen thermal plasma generated by a non-transferred DC arc plasma torch was used to decompose tetrafluoromethane (CF₄). In the thermal decomposition process, water was used as a chemical reactant source. Two kinds of water spray methods were compared: water spray directly to the arc plasma flame and indirectly to the reactor tube wall. Although the same operating conditions of input power, waste gas, and sprayed water flow rate were employed for each water spray methods, a relatively higher decomposition rate was achieved in the case of water spray to the reactor wall. In order to investigate the effects of water spraying direction on the thermal decomposition process, a numerical simulation on the thermal plasma flow characteristics was carried out considering water injection in the reactor. The simulation was performed using commercial fluid dynamics software of the FLUENT, which is suitable for calculating a complex flow. From the results, it was revealed that water spray to the reactor wall and use of a relatively small quantity of water are more effective methods for decomposition of CF₄, because a sufficiently high temperature area and long reaction time can be maintained over large area.     

使用发射光谱对H2稀释情况下的感应耦合H2/C4F8等离子体中碳氟基团的研究

在射频输入功率为400W，气压为0.8Pa的条件下，使用光强标定的发射光谱方法研究了感应耦合H₂/C₄F₈等离子体中CF, CF₂, H和F基团的相对密度随流量比R=H₂/(H₂+C₄F₈)的变化情况，而HF基团相对密度的变化由四级质谱仪探测得到。结果表明等离子体活性先随着R的增加而升高，然后随着R的进一步增加而下降。在流量比从0逐渐上升到0.625的过程中，CF和CF₂基团的相对密度不断降低。实验中测得的CF基团的相对密度[CF]与理论计算得到的[CF]有很好的一致性说明了电子与CF2基团的碰撞反应是CF基团产生的主要原因。文中还讨论了HF基团。     

A hybrid variational–perturbational nuclear motion algorithm

A hybrid variational–perturbational nuclear motion algorithm based on the perturbative treatment of the Coriolis coupling terms of the Eckart–Watson kinetic energy operator following a variational treatment of the rest of the operator is described. The algorithm has been implemented in the quantum chemical code DEWE. Performance of the hybrid treatment is assessed by comparing selected numerically exact variational vibration-only and rovibrational energy levels of the C₂H₄, C₂D₄, and CH₄ molecules with their perturbatively corrected counterparts. For many of the rotational–vibrational states examined, numerical tests reveal excellent agreement between the variational and even the first-order perturbative energy levels, whilst the perturbative approach is able to reduce the computational cost of the matrix-vector product evaluations, needed by the iterative Lanczos eigensolver, by almost an order of magnitude.     

Contributions of Spin–Lattice Relaxation to the Echo Decay of Planar Cu in High-Temperature Superconductors

Measurement ofT_2G, the Gaussian component of the spin-echo envelope of planar Cu nuclei in high-temperature superconductors, gives important information about the real part of the Cu electron spin susceptibility. In the traditional picture of the planar Cu echo decay, the internuclear coupling is assumed to remain static with respect to spin–lattice relaxation and mutual exchange fluctuations. In some circumstances, however, this assumption breaks down. We calculate the internuclear corrections arising from spin–lattice relaxation to the conventional theory ofT_2Gand show thatT_2Gcan be easily corrected for these effects. We argue that mutual exchanges due to the perpendicular indirect couplings are suppressed in these materials. For YBa₂Cu₄O₈, we find a correction on the order of 10% inT_2Gand using the corrected values we find that the isotope ratio⁶³T_2G/⁶⁵T_2Gagrees with theory.     

On the isotope effect of Tc in squaric acid (H2C4O4)

The phase transition mechanism in squaric acid is reviewed from the viewpoint of the pressure dependence of the O—H—O bond length (2R). The two-dimensional pressure effect on T_c is extracted from the hydrostatic pressure behaviour by taking account of the uniaxial stress applied perpendicular to the layer planes. The result shows that if 2R(H₂SQ) is stretched to 2R(D₂SQ) the phase transition temperature 7^H _c of H₂SQ coincides with T^D _c of D₂SQ. This result supports the suggestion that the phase transition mechanism is of the order-disorder type.     

Reasons for the deactivation of Pt/TiO2 photocatalyst treated by inert gas N2

The effect of N₂ treatment on the photocatalytic activity of Pt⁰/TiO₂ was investigated. The results showed that after treatment at 500 °C in N₂, 70% of the photocatalytic activity of 1.0 wt.% Pt⁰/TiO₂ was lost by the evaluation of photocatalytic oxidation reaction of C₃H₆. Transmission electron microscopy (TEM) and Ar⁺ ion sputtering tests revealed that in the course of high-temperature N₂ treatment, the size of Pt⁰ particles on TiO₂ increases and a strong interaction between metal and support, i.e. Pt⁰ particles encapsulated by Ti_xO_y, happens, which are the reasons for the deactivation of Pt⁰/TiO₂ photocatalyst treated by high-temperature N₂.     

Determination of blood longitudinal relaxation time (T1) at high magnetic field strengths

In this study, a circulation system was used to measure T(1) values of bovine blood under physiological conditions at field strengths of 4.7, 7 and 9.4 T. Results show that T(1) increases linearly with magnetic field B(0) and can be described with the equation T(1)=129 ms/T B(0)+1167 ms for magnetic field strengths between 1.5 and 9.4 T.     

High T c superconductors as ionic metals and the role of phonons in high T c superconductivity

We have investigated a number of zone center and zone boundary (X-point) modes in La₂CuO₄ using the full potential Linearized Augmented Plane Wave (LAPW) method and find excellent agreement with experiment for phonon frequencies, showing that the local density approximation (LDA) is an excellent approximation for the total energies, charge density, and static density response in high T _c superconductors. Results are compared with those of a non-empirical ionic model for La₂CuO₄ and YBa₂Cu₃O₇. Self-consistent calculations show that the ionic nature of these materials leads to large changes in the potential with atomic displacements. The ionic contributions to the electron-phonon matrix elements, which were neglected in previous studies, are large and possibly sufficient to explain high T _c .     

Review of quantitative spectroscopy of polyynes

We propose a review of quantitative spectroscopy of polyynes in the infrared and ultraviolet domain focusing on essential spectroscopic parameters for the interpretation of observed spectra in the infrared and ultraviolet domain and for photochemical modeling. We point at the lacking data in both wavelength domains for C₂H₂, C₄H₂, C₆H₂, C₈H₂ and propose downloadable files of the ultraviolet absorption coefficient ready to use for photolysis rate calculations. For longer polyynes, we calculate extrapolated ultraviolet spectra and calculate their photolysis rate. Using a simplified photochemical model of the polyynes in Titan and CRL618, we predict their relative abundance and compare them with the observed ones. This also leads us to predict the abundances of the longer polyynes.     

NQR Study of Phase Transition and Cationic Motion in 4-NH2C5H4NHBiBr4·H2O

Four ⁸¹Br NQR lines in 4-NH₂C₅H₄NHBiBr₄·H₂O were observed in the temperature range between 77 and ca. 380 K; with increasing temperatures the respective sets of higher and lower two resonance lines coalesced into single lines discontinuously at 274 K, showing the occurrence of a first-order type phase transition of this crystal. The transition was confirmed with heat anomaly on a DTA curve. Each higher and lower line of high-temperature phase is assignable to the terminal Br atoms and the bridging ones of one-dimensional poly anions (BiBr₄ ⁻) _n in the crystal structure (C2/c), which was investigated by a X-ray structure analysis at room temperature. The 1/T ₁ temperature dependence of ⁸¹Br NQR follows the usual T ² law in the temperature range between 77 and ca. 140 K, being explained by fluctuation of the EFG at Br nucleus due to lattice vibrations. The T ₁ vs. 1/T curve in the temperature range between about 160 and 190 K was describable by the exponential curves, allowing us the estimation of activation energies. These exponential behaviors of T ₁ of ⁸¹Br NQR are attributable to the fluctuations caused by the thermal motion of 4-NH₂C₅H₄H⁺ ions. Echo signals of the ⁸¹Br NQR could not be detected above 190 K owing to poor S/N with very short T ₂.