Alignment of non-polar molecules—electric field effects in the 2H N.M.R. spectrum of perdeuterobenzene in solutions with nitrobenzene

Electric field experiments on the ²H N.M.R. spectrum of perdeuterobenzene, dissolved in nitrobenzene, are reported. The alignment of the polar molecules, induced by a strong electric field, is transferred to the non-polar ones and as a result their N.M.R. spectrum is modified.

Local field models, e.g. those of Lorentz and Onsager, treat the environment of a molecule as a continuum and are unable to explain the alignment of the non-polar molecules. Intermolecular interactions are essential. In an expression for the alignment these interactions are described in terms of correlation functions for the mixture.

N.M.R. and Kerr data of nitrobenzene-benzene solutions have been compared. The Kerr constant of a binary mixture is shown to depend on the alignments of both the polar and non-polar component. N.M.R. electric field experiments may be useful to separate these two contributions.     

Synthesis and Spectroscopic Studies of Some New Polyether Ligands of the Schiff Base Type

Abstract

New polyether ligands of Schiff base type (3–13) were synthesized from the reaction of diethylene glycol bis(2‐aminophenyl)ether and triethylene glycol bis(2‐aminophenyl)ether with salicylaldehyde, 5‐methoxysalicylaldehyde, 5‐bromosalicylaldehyde, 5‐nitro salicylaldehyde, and 2‐hydroxy‐1‐naphthaldehyde. The products were characterized by elemental analysis, IR, ¹H, ¹³C NMR, and UV‐VIS techniques. The UV‐VIS spectra of those Schiff bases with an OH group in the ortho position to the imino group were studied in polar and nonpolar solvents in acidic and basic media. The compounds are in tautomeric equilibrium (enol‐imine, O–H · N?keto‐amine, O · H–N forms) in solvents, acidic chloroform, and benzene solutions and basic DMSO, chloroform, and benzene solutions. These tautomers were not observed in polar and non‐polar solvents and in basic solutions of DMSO, chloroform, and benzene for the Schiff bases 5–10. Tautomer proportions, which were obtained from ¹H NMR and UV‐VIS data in DMSO, were compared for compounds 3, 4, 11, and 12.     

75As N.Q.R. and 19F N.M.R. study of solid AsF3

The temperature dependence of the ⁷⁵As pure quadrupole resonance frequency in AsF₃ has been studied from 77 K to a temperature very close to the melting point. It is found that the effective electric field gradient at the As site does not shift much from the gas-phase value and that the temperature dependence of the ⁷⁵As N.Q.R. frequency seems to follow the Bayer-Kushida model. The occurrence of a line-width transition in the ¹⁹F N.M.R. spectrum between 200 and 150 K demonstrates the presence of low-frequency, large-amplitude molecular motions which are too slow to average out the ⁷⁵As quadrupole coupling.     

Frequency dependence of the nonlinear dielectric effect in diluted dipolar solutions

The nonlinear dielectric relaxation in dilute solutions of strongly polar molecules (4,4′-n-hexylcyanobiphenyl) in nonpolar medium (benzene) has been investigated. The nonlinear dielectric increment, induced by a d.c. electric field of high intensity (Eo ≈ 10⁷ V/m), was detected with an a.c. field of small intensity and variable frequency (1 MHz-3 GHz). The relaxational behavior of the increment is discussed in the framework of the theory proposed by Coffey et al.     

Magnetic Moment of Fe and Magnetocrystalline Anisotropy of Fe-rich Intermetallic Compounds Under Pressure

Magnetization and magnetocrystalline anisotropy of Fe-rich R -Fe intermetallics ( R =Y and rare earths) have been studied under pressure up to 1 GPa in temperatures from 5 K to 350 K using a miniature CuBe pressure cell and a SQUID magnetometer. A decrease of Fe-moment under pressure depends strongly on local environment parameters such as a local atomic volume, local coordination of Fe-atoms and hybridization. The pressure-induced changes of magnetocrystalline anisotropy energy are caused by both, the pressure decrease of magnetization M S and the pressure effect on the crystal electric field interactions. The pressure experiments allow to distinguish both the effects.     

1H and 2D N.M.R. studies of the radical anions of biphenyl,fluorenone and phenanthrene

The proton N.M.R. spectra of biphenyl^-, fluorenone^- and phenanthrene^- and the deuterium N.M.R. spectra of biphenyl-d10^- and phenanthrene-d10^- have been measured in ethereal solutions at room temperature. Sign and magnitude of the hyperfine splitting constants derived from the measured contact shifts are reported and compared with E.S.R. data and predictions from theory. From the measured proton and deuterium relaxation times values for the electron spin and the rotational correlation times have been obtained.     

Dielectric-field effect correction on i.r. band shapes in the liquid phase

The dielectric-field correction on i.r. band shape in the liquid has been studied by using the Lorentz internal field. The deformation of the band shape is inappreciable for a weak absorption band that becomes measurable only at a sample thickness larger than 10μ. The shapes of the strong singlet and doublet bands of hexafluorobenzene at 1530 cm^?1 and near 1000 cm^?1, respectively, and also of the doublet band of carbon tetrachloride near 790 cm^?1 have been measured in dilute solutions and compared with those for the pure liquid.     

Zur mikrophysikalischen Beschreibung des schwachionisierten Säulenplasmas von Glimmentladungen in Stickstoff-Neon-Gemischen III. Bilanzierung des Säulenplasmas und Berechnung seiner inneren Parameter

For the plasma of the low current positive column in the N,-Ne-mixture the equations for the concentration of different kinds of ions and excited particles are set up. The axial electric field strength, the degree of ionization and the concentration of excited Ne-atoms and of the different kinds of ions are calculated by simultaneous solution of these balances together with the electron Boltzmann equation for this mixture and the balances for the electric current and quasineutrality of the column plasma. All these macroscopic properties of the discharge column are investigated for electric currents of 0.5 mA to 13,5 mA, for total pressures of 0,37 torr to 3,7 torr and for any mixture ratio. A comparision between measured and calculated electric field strengths shows a good agree-ment. The ionization of the N,-molecules by collisions with the metastable Ne-atoms (Penning-ionization) is of great significance for the generation of new charge carriers in such a mixture. In these investigations the collision rate zp of the Penning-ionization was obtained to 3 · 10^?11 cm³ s^?1 by the aid of a comparision between measured and calculated electric axialgradients of the column.     

An electron paramagnetic resonance study of nitrogen dioxide dissolved in water, carbon tetrachloride and some organic compounds

Electron paramagnetic resonance spectrometry was used to characterize and measure the concentration of nitrogen dioxide dissolved in water, carbon tetrachloride, n-hexane, acetone and benzene at 290 K. Solutions were monitored by ultraviolet spectrometry. We measured the equilibrium constant for N₂O₄ plus NO₂ dissolved in n-hexane and carbon tetrachloride. In order to investigate the formation of organic nitroxide type intermediates, some experiments were designed to examine the role of NO and NO plus NO₂ mixtures.     

Ion Mobility Measurements of Carbon Tetrachloride

Abstract

The ion mobility and drift velocity of carbon tetrachloride have been measured at various ratios of E/P_o, ranging from 1.0 to 9 volts/ (cm-Torr). The technique employed for these measurements utilizes a polonium alpha particle source which serves both as the source for ionization as well as the means for producing a reference pulse from a solid state silicon barrier detector. The thermal electrons which are produced are readily captured by carbon tetrachloride and the resulting negative ion, assumed to be CC1₄ ^?, is detected by means of a proportional counter located at the end of the drift path. The zero field reduced mobility obtained for CC1₄ ^?was 0.42 cm²/(volt-sec). The nature of the ionic species is explained in terms of the quantum mechanical theory of ionic mobility as put forth by Dalgarno.     

A comparative study of non-polar solvents effect on dielectric relaxation and dipole moment of binary mixtures of mono alkyl ethers of ethylene glycol and of diethylene glycol with ethyl alcohol

Dielectric relaxation and dipole moment of binary mixtures of homologous series of mono alkyl ethers of ethylene glycol and of diethylene glycol, i.e., mono methyl, mono ethyl and mono butyl ethers of ethylene glycol (ROCH₂CH₂OH) and mono methyl, mono ethyl and mono butyl ethers of diethylene glycol (ROCH₂CH₂OCH₂CH₂OH) with ethyl alcohol (C₂H₅OH) of different concentrations were studied in dilute solutions of benzene, dioxane and carbon tetrachloride at 35 °C. Permittivity (ε′) and loss (ε″) at 10.1 GHz, static dielectric constant ε_o at 1 MHz and high frequency limiting dielectric constant ε_∞ = n_D² at optical frequency of these molecules and their binary mixtures at different concentration were measured in dilute solutions of non-polar solvents. The average relaxation time τ_o, relaxation times corresponding to overall molecular reorientation τ₁ and group rotations τ₂ were determined using Higasi's single frequency measurement equations for dilute solutions. The evaluated values of relaxation times and free energy of activation ΔF were used to explore the solvent effect on molecular dynamics of these polar binary systems in non-polar solvents. The excess inverse relaxation time and excess free energy of activation were determined to confirm the existence of hydrogen-bonded heterogeneous cooperative domains of the ethers and alcohol molecules at different concentration their binary mixtures in non-polar solvents. The dipole moment of the binary mixtures was evaluated using Higasi's and Guggenheim's equation for dilute solutions. The evaluated values of dipole moments and computed dipole moment values using a simple mixing equation of the polar molecules binary mixture were used to explore the effect of non-polar solvent environment on heterogeneous molecular interactions between ethers and alcohol molecules. The effect of number of carbon atoms in the molecular structure of these homologous series molecules was also considered for the interpretation of various evaluated dielectric parameters.     

A Dual 13C and 15N Long Term Labelling Technique to Investigate Uptake and Translocation of C and N in Beech (Fagus sylvatica L.)

Abstract

A continuous dual ¹³CO₂ and ¹⁵NH₄ ¹⁵NO₃ labelling experimental set-up is presented that was used to investigate the C and N uptake and allocation within 3-year old beech (Fagus sylvatica L.) during one growing season. The C and N allocation pattern was determined after six, twelve and eighteen weeks of growth. The carbon uptake was distinctly different in the three phases examined: The first six weeks after budbreak were dedicated to leaf growth with a R/S (root to shoot) ratio of 0.14 for the new carbon. The second growth phase showed a balanced R/S ratio of C allocation and after week 13, the root compartment was the main carbon sink (R/S = 6.97).

Nitrogen allocation was more basipetal as compared to carbon. In the second growth phase, R/S of N_new was 5.57 but fell to 3.54 for the third growth phase probably due to formation of reserves in buds and stem.     

Alignment of polarizable dipoles on a lattice

The alignment average of polar molecules may be derived from their NMR spectrum, when a strong electric field is applied to the liquid. The Kerr effect can likewise be related to the alignment.In this paper the alignment has been calculated for a rigid-lattice model, previously developed by Van Vleck in the theory of dielectric polarization and extended by others. A series expansion of the alignment for a system of isotropically polarizable dipoles is presented up to second-order terms in the dipolar interaction. The result for a continuum has been compared with those calculated on the basis of the Lorentz and Onsager model of the liquid.An explicit expression for the total electrostatic energy of a binary mixture of polar and non- polar molecules with a symmetric polarizability tensor has also been calculated; it has been obtained from a generalization of a formalism, developed by Mandel and Mazur for the pure polar liquid.     

丝网印刷制备碳纳米管阴极的强流脉冲发射特性研究

采用丝网印刷法制备了一种大面积的碳纳米管阴极,表征了阴极表面碳纳米管的形貌及分布.研究了该阴极在不同脉冲条件下的高压脉冲发射特性,分析了发射时阴极面等离子体产生和发射点的分布.研究表明：碳纳米管阴极的脉冲发射机制为爆炸电子发射,在平均场强为16.7V/μm的单脉冲电场下,阴极的最高发射电流密度为99 A/cm².在平均场强为15.4 V/μm的双脉冲电场下,阴极的最高发射电流密度为267 A/cm².碳纳米管阴极可以作为强流电子束源在高能微波器件中得到应用. 关键词： 强流脉冲电子束 碳纳米管 阴极 丝网印刷     

Hydrocarbon ions with triplet ground states

The N.M.R. spectra of meta dichloro and meta dibromo benzenes are analysed in the nematic phase of 4-methoxy benzylidene-4-amino-α-methyl cinnamic acid-n-propyl ester at room temperature.

The direct couplings are found to be of negative sign. The molecules orient preferentially with the aromatic plane along the direction of the magnetic field and the C ₂-symmetry axis perpendicular to it.

The relations between the various direct couplings and the inter-proton distances are reported. The ratio of the distance between the meta protons along the axis perpendicular to the C ₂ symmetry and the ortho protons is determined precisely. The other ratios could not be determined to any reasonable precision. The reasons are discussed.

The angles between the C-H bonds of the equivalent protons and the C-C bonds in both the molecules are determined on the assumption of the C-H bond lengths and the ring geometry of benzene.     

NMR spin-lattice relaxation of the129Xe nucleus of xenon gas dissolved in various isotropic liquids

The spin-lattice relaxation time of the¹²⁹Xe nucleus of natural xenon gas dissolved in various isotropic liquids, acetonitrile, benzene, carbon tetrachloride and cyclohexane, was studied as a function of temperature at the magnetic fields of 9.4 and 4.7 T. The utilization of hydrogenated and deuterated benzene and cyclohexane reveals that the intermolecular¹²⁹Xe-¹H dipole-dipole interaction constitutes an important relaxation mechanism in hydrogenated solvents. According to this interpretation the interaction is rather strongly temperature-dependent, and increases with increasing temperature. An important observation of an experimental nature is also noted, namely convective flow present in non-spinning sample tubes at elevated temperatures disturbs inversion-recovery measurements and leads to erroneous and unreliable relaxation time values.     

Parameters of LC molecules’ movement measured by dielectric spectroscopy in wide temperature range

Dielectric properties of a nematic liquid crystal (NLC) mixture ZhK-1282 were investigated in the frequency range of 10²–10⁶Hz and a temperature range of ?20 to 80?°С. On the basis of the Debye’s relaxation polarization model dielectric spectra of temperature dependence of the orientational relaxation time τ and the dielectric strength δe were numerically approximated at the parallel orientation of a molecular director relative to alternating electric field. Influence of ester components in the mixture plays crucial role in relaxation processes at low temperature and external field frequency. The activation energy of the relaxation process of a rotation of molecules around their short axis was measured in a temperature interval of ?20 to ?+15?°С in which the dispersion of a longitudinal component of the dielectric constant takes place. The energy of potential barrier for polar molecules rotation in the mesophase was calculated. The value of the transition entropy from the nematic to isotropic phase was obtained from this calculation. The values of the coefficient of molecular friction and rotational diffusion were obtained by different methods. The experimental data obtained are in a satisfactory agreement with the existing theoretical models.     

Structural and 14N EFG Information on Solid Imidazole by 13C CP/MAS NMR Data

Residual dipolar coupling between carbons and ¹⁴N nuclei in the ¹³C CPMAS NMR spectrum of solid imidazole is studied. Calculations of expected splittings with a previously reported equation leads to the complete assignment of the solid state carbon chemical shifts. Additionally, information is provided on the location of ¹⁴N electric field gradient axes at the N-H site.     

Electric birefringence of solutions of nematic compounds

The static field Kerr electro-optic effect has been studied in solutions of the nematic liquid crystals MBBA and PCB in carbon tetrachloride. These compounds are negative and positive nematics respectively. At low field strengths, all solutions exhibited Kerr law behaviour and Kerr constants were evaluated. The dependence of these constants on concentration differed markedly between these two nematic materials. With MBBA, the birefringence and hence the Kerr constant underwent a reversal of sign from positive to negative with increasing solution concentration. With PCB, the Kerr constant was always positive. Whereas MBBA solutions always showed Kerr law behaviour for fields up to 45 kV cm^-1, the PCB solutions showed deviations from this at the higher field strengths. Combinations of higher concentrations and field strengths resulted in irregular transients in the birefringence.     

Comparison and semiconductor properties of nitrogen doped carbon thin films grown by different techniques

Amorphous carbon nitride (a-CN_x) thin films have been synthesised by three different deposition techniques in an Ar/N₂ gas mixture and have been deposited by varying the percentage of nitrogen gas in the mixture (i.e. the N₂/Ar + N₂ ratio) from 0 to 10%. The variation of the electrical conductivity and the gap values of the deposited films versus the N₂/Ar + N₂ ratio were investigated in relation with their local microstructure. Film composition was analysed using Raman spectroscopy and optical transmission experiments. The observed variation of electrical conductivity and optical properties are attributed to the changes in the atomic bonding structures, which were induced by N incorporation, increasing both the sp² carbon content and their relative disorder. The low N content samples seem to be an interesting material to produce films with interesting properties for optoelectronic applications considering the facility to control the gas composition as a key parameter.