On the magnetic properties of Lithium Vanadium Bronzes LixV2O5

Magnetic susceptibility of V₂O₅ and of the α-, ?-, δ- and γ-Li_xV₂O₅ bronzes prepared either at high or at room temperature has been measured between liquid helium and ambient temperature. The results are representative of the localized character of the V⁴⁺ ion d-electron and, for high enough x-values, of the existence of antiferromagnetic interactions in a low dimensional system. The intrachain exchange integral J has been determined using the Bonner/Fischer model for Heisenberg chains with S = 1/2 spin. It is larger for the γ- than for the δ-phase. This result as well as the occurrence of long range ordering below T_N ≈ 130 K in the γ-phase may be ascribed to ordering of V⁴⁺ and V⁵⁺ ions in the former bronze and to the random distribution of V⁴⁺ ions in the latter one.     

Dynamic metal-ligand coupling in the infrared MCD spectra of the cobalt(II) tetrahalides

The axial single-crystal magnetic circular dichroism spectra of Cs₃ZnCl₅/Co²⁺ and Cs₃ZnBr₅/Co²⁺ have been measured over the 4000–7000 cm^?1 region of the ⁴A₂ → ⁴T₁ (F) transition at ambient and liquid-helium temperature. The B/D and C/D terms obtained give transition moment ratios, 〈t₂∥m∥t₂〉/〈e∥m∥t₂〉, in accord with the value required (?3^{$\text{1}\text{2}$}/2^{$\text{1}\text{2}$}) by a dynamic ligand-polarisation model for d-electron transition probabilities in tetrahedral metal complexes.     

Proton NMR study of molecular dynamics in ammonium tribromo stannate (NH4SnBr3)

The proton second moment M₂ and spin-lattice relaxation time T₁ have been measured in ammonium tribromo stannate (NH₄SnBr₃) in the temperature range 77–300 K, to determine the ammonium dynamics. The continuous wave signal is strong and narrow at 77 and 300 K but has revealed an interesting intensity anomaly between 210 and 125 K. T₁ shows a maximum (13 s) around 220 K. No minimum in the T₁ vs 1000/T plot was observed down to 77 K. M₂ and T₁ results are interpreted in terms of NH⁺₄ ion dynamics. The activation energy E_a for NH⁺₄ ion reorientation is estimated to be 1.4 kcal mol⁻¹.     

The Natural Optical Activity of Tris(Ethylenediamine)Metal(II) Nitrates V. The Single Crystal Circular Dichroism Spectrum of Ni(en)3 (NO3 )2

The axial CD spectra of single crystal of Zn(en)₃(NO₃)₂ doped with 1-50% Ni(en)₃(NO₃)₂ have been observed at temperatures from ambient to 5 K. The increase in R of the ³E[³T_3g(F)] transition as the temperature decreases is consistent with the magnetic dipole allowed character of the parent octahedral transition. The electric and magnetic dipole forbidden transition to the ³T_1g(F) octahedral level gives rise to a relatively weak axial CD band with an unusual temperature dependent splitting. This structure is attributed to electric quadrupole intensity, which is allowed for transitions to both the E and ³A₂[³T_1g(F)] levels in D₃ symmetry.     

Friccohenics of Continuum and Non‐Continuum Models for Liquid Flow Applied for Heteromolecular Interaction of DNA Bases and Sugars Estimated with Mansingh Equation

Newtonian and non‐Newtonian liquids widely characterize continuum and non‐continuum models for flows, thus, viscous (continuum) and drop wise (non‐continuum) flows of water and aqueous nucleotides (2‐deoxy adenosine‐DOA, thymidine‐TMD) and nucleosides (guanosine monophosphate‐GMP, adenosine triphosphate‐ATP) with integral unites‐2‐deoxy ribose‐DOR (referred as DNA bases and sugars) have been studied with Survismeter. Time data for viscous (t and drop wise (dt) flows along with drop counts (n) for aqueous solutions of 0.4–1.4 millimol (mm) DNA base and sugars with survismetere at 288.15, 293.15, and 298.15 K are measured for viscosities and surface tension, respectively. The t and n are fitted in Mansingh equation for Friccohesity (σ) calculation that determines dipole moment (µ). The t, dt, and n data are measured for water from 15 to 70°C at an interval of 5°C for standard equation for dipole moment calculation. The t, dt and n values decrease with temperature where the σ is directly proportional to μ values with slight increase with compositions and decreases with temperatures. A continuous decrease in μ values with compositions is noted with slightly higher decrease at 288.15 with both millimol and temperature. The higher decrease with temperatures weakens Coulombic forces ((q₁ · q₂)/r², with charges q₁ and q₂, and radii r)) where σ increase.     

Influence of electrostatic interactions on the properties of cyanobiphenyl liquid crystals predicted from atomistic molecular dynamics simulations

The influence of force field details in all-atom molecular dynamics (MD) simulations on the predicted thermodynamic, structural, and dynamic properties of bulk 4-cyano-4?-pentylbiphenyl (5CB) systems have been investigated in the 292–368 K temperature range. The effect of the molecular dipole moment and the details of dihedral potential for biphenyl unit were investigated using both polarisable (POL) and non-polarisable (NP) versions of the quantum chemistry-based force field. The predicted densities for the nematic and isotropic phases of bulk 5CB were found to be in excellent agreement with available experimental data. The nematic-isotropic transition temperature (T_NI) showed strong sensitivity to the force field details, MD simulations with partial atomic charge distributions and molecular dipole moment corresponding to high-level quantum chemistry calculations predicted an overestimation of the T_NI by about 30 K. Rescaling the charges to allow the molecular dipole to be closer to experimentally reported values of 5CB dipole in condensed phases, significantly improved the prediction of T_NI as well as other thermodynamic and dynamic properties of 5CB. We also discuss how the structural, thermodynamic, and dynamic properties of bulk 5CB are affected by the flexibility of the central biphenyl dihedral and the inclusion of induced polarisation effects.     

Determination of transition moments from power saturation

The electric (or magnetic) dipole transition moment may be calculated from the power broadening of saturation spectra if the ratio (T₂/T₁) is known or can be assumed as unity. The transition moment of the (43-0) P(13) R(15) lines of I₂ coincident with the 5145 Å Ar⁺ laser line is calculated from literature data on the power broadening of the saturation spectrum and compared to that obtained from absorption intensity measurements.     

The effect of molecular polarity on nem/catic phase stability in 12-vertex carboranes

Weakly polar–polar isosteric pairs of 12-vertex p-carborane [closo-1,12-C₂B₁₀H₁₂] (1[12]) and monocarbaborate [closo-1-CB₁₁H₁₂]^? (2[12]) nematic liquid crystals, in which the difference in the calculated molecular dipole moment is 11.3 D, were synthesised, and the effect of the dipole moment on nematic phase stability was investigated. The trend observed for the 12-vertex series ([12]) was identical to that of the previously investigated 10-vertex series ([10]) containing [closo-1,10-C₂B₈H₁₀] (1[10]) and [closo-1-CB₉H₁₀]^? (2[10]): the uniform increase in the molecular dipole moment in the pairs of mesogens does not correspond to a uniform change in the clearing temperature, T_NI. This demonstrates the role of a remote substituent in modulating the intermolecular dipole–dipole interactions. The magnitude of such interactions was calculated (using density functional theory methods) for a pair of polar (2[12]d–2[12]d) and an analogous pair of weakly polar (1[12]d–1[12]d) molecules. All results for the 12-vertex series ([12]) were analysed relative to the 10-vertex analogues ([10]).     

Single-photon ionisation of TMPD in liquid CCl4 observed by time-resolved microwave conductivity

A large microwave conductivity change is observed on laser flash photolysis (308 nm) of a solution of TMPD in CCl₄. This is ascribed to single-photon ionisation of the solute resulting in the formation of a stable TMPD⁺Cl^? ion pair. The dipole moment of the ion pair is estimated to be (8.7 ± 0.9)(φ*)^{?$\text{1}\text{2}$} where φ* is the quantum efficiency for ion-pair formation.     

Studies in negative ion mass spectrometry. X—Electron capture by a series of tris(hexafluoroacetylacetonato) metal chelates

Results of electron capture and negative ion mass spectrometric studies are reported for a series of tris-chelates of the type Metal. L₃, where L refers to the ligand or enolate ion of the β-diketone 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hexafluoracetylacetone), and the metals are: Sc(III), Ti(III), V(III), Cr(III), Mn(III), Fe(III), Co(III), A1(III), Ga(III), In(III). The negative ion mass spectra were all relatively simple; the most abundant ions being the molecular and ligand ions for all the metals studied. Reaction schemes have been established to account for the appearance of all significant fragment ions, many of which have been formed as a result of fluorine atom transfer processes. For the transition metal complexes, evidence for elimination of neutral divalent metal fluorides comes from the ion decomposition reactions [Metal.L.F₂]^?→[L]^?, and for the Group III metal complexes, [Metal.L₃]^?→[Metal.L₂]^? as well as [Metal.L₂]^?→[L]^? processes indicate that the metals have been reduced as a consequence of the initial electron capture and subsequent fragmentations of metal-containing ions. The influence of the metal atom and its 3d-electron configuration has been shown not to affect significantly the electron capture processes. However, the relative instabilities of molecular anions of the transition metal tris-complexes show an approximately linear dependence on the increasing 3d-electron populations of the metal ions from Ti(III) to Co(III).     

Optimization of the electron spin resonance spectrometric determination of transition-metal ions by variation of temperature

The effect of variation in temperature on the first-derivative electron spin resonance spectra of transition metal ions in aqueous solution is reported. For the aquo ions of Mn(II), Cr(III), Fe(III) and vanadyl, and for hexafluoroferrate(III), an increase in temperature results in a decrease in line width with a concomitant increase in signal amplitude. In contrast, [Cu(H₂O)₆]²⁺ and [Ti (H₂O)₄F₂]⁺ show an increase in line width and a marked decrease in derivative amplitude as the temperature is raised. Consequently, the choice of the optimum temperature for each system results in greatly improved sensitivity and lower limits of detection. Recording spectra at more than one temperature is also useful for detecting a given metal ion in a multicomponent system that has overlapping resonance lines.     

Aurivillius phases of PbBi4Ti4O15 doped with Mn synthesized by molten salt technique: Structure, dielectric, and magnetic properties

Doping of manganese (Mn³⁺/Mn⁴⁺) into the Aurivillius phase Pb_1−xBi_4+xTi_4−xMn_xO₁₅ was carried out using the molten salt technique for various Mn concentrations (x=0, 0.2, 0.4, 0.6, 0.8, and 1). Single phase samples could be obtained in the composition range with x up to 0.6 as confirmed by X-ray and neutron diffraction analysis. Dielectric measurements show a peak at 801, 803, 813 and 850 K for samples with x=0, 0.2, 0.4, and 0.6, respectively, related to the ferroelectric transition temperature (T_c). The main contribution of the in-plane polarization for x≤0.2 which was calculated from the atomic positions obtained by the structure analysis is the dipole moment in the Ti(1)O₆ layer; however, for x≥0.4 the polarization originates from the dipole moment in the Ti(2)O₆ layer. Mn doping in the Pb_1−xBi_4+xTi_4−xMn_xO₁₅ does not show any long range magnetic ordering.     

Molecular electric properties in electronic excited states: multipole moments and polarizabilities of H2O in the lowest1 B 1 and3 B 1 excited states

Summary The dipole and quadrupole moments and the dipole polarizability tensor components are calculated for the¹ B ₁ and³ B ₁ excited states of the water molecule by using the complete active space (CAS) SCF method and an extended basis set of atomic natural orbitals. The dipole moment in the lowest¹ B ₁ (0.640 a.u.) and³ B ₁ (0.416 a.u.) states is found to be antiparallel to that in the ground electronic state of H₂O. The shape of the quadrupole moment ellipsoid is significantly modified by the electronic excitation to both states investigated in this paper. All components of the excited state dipole polarizability tensor increase by about an order of magnitude compared to their values in the ground electronic state. The present results are used to discuss some aspects of intermolecular interactions involving molecules in their excited electronic states.     

Hydrogen bond CH…O in a methanolic solution of hydrogen chloride

The existence of a hydrogen bond in which a methyl group of the (MeOH)₂H⁺ ion acts as a proton donor is examined. The fundamental vibration frequencies of this ion were calculated for different numbers and strengths of CH…O bonds. The atomic charges in neutral ((MeOH) _n ,n=1–4) and protonated ((MeOH) _m H⁺,m=2–6) associates of methanol molecules were also calculated. The experimentally observed decrease in the v(CH) vibration frequencies of the (MeOH)₂H⁺ ion to 2890 cm⁻¹ and 2760 cm⁻¹ is attributable to the fact that each methyl group of the ion is involved in formation of two CH…O bonds with strength of −12.5 kJ mol⁻¹. The proton-donating ability of the CH bond depends on the charge on its H atom; however, it does not correlate with the dipole moment of this bond. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 306–312, February, 1999.     

Vibrational radiative lifetimes in H2Se and HCS−

Vibrational dipole matrix elements and radiative transition probabilities for H₂Se and HCS⁻ have been evaluated from theoretical three-dimensional electric dipole moment and potential energy functions. The radiative lifetimes of the (v=1,J=0) levels of HCS⁻ have been calculated to be 3.5 ms (CH stretch), 172 ms (HCS bend) and 785 ms (CS stretch), and in H₂Se to be 122 ms (symmetric stretch), 1045 ms (bend) and 101 ms (asymmetric stretch). The lifetimes of higher vibrational states with no extensive mode-mixing decrease with increasing vibrational quantum number and vary in a mode-specific way.     

Dielectric and viscous properties of 6CHBT in the isotropic and nematic phases

This paper presents the results of measurements of the principal electric permittivities ε ∥_*(T, ω and ε⊥*(T, ω) and the viscosity for 4-(trans-4-n-hexylcyclohexyl)isothiocyanatobenzene (C₆H₁₃-CyHx-Bz-N=C=S, 6CHBT). In the nematic phase, the Miesowicz η₂ viscosity coefficient was measured in a sample oriented due to the flow. On the basis of the temperature dependence of the static permittivities, using the Maier-Meier equations, the angle β between the dipole moment vector and the long axis of the 6CHBT molecule, the square of the molecular apparent dipole moment μ² _app ² and the nematic order parameter S(T), were determined. From the temperature dependence of the viscosity and the relaxation time corresponding to the molecular rotation around the short axis, the strength of the nematic potential and the effective length of the 6CHBT molecule (in the isotropic phase) were estimated.     

Dielectric properties of 1,1,1-trifluoroethane (HFC-143a) in the liquid phase

The relative permittivity (?_r) data of 1,1,1-trifluoroethane (HFC-143a), (CAS N# 420-46-2), a hydrofluorocarbon (HFC) developed as a refrigerant that has zero ozone depletion potential, is reported. The relative permittivity of HFC-143a in the liquid phase was measured using a direct capacitance method at temperatures from T = 218 to 294 K and at pressures up to P = 15 MPa, for a frequency of 10 kHz. The uncertainty of the ?_r measurements is estimated to be better than ±1.2 × 10⁻². A complete set of tables of experimental data as a function of temperature, pressure and density, is presented that covers the dielectric property needs for most engineering applications. To study the dependence of ?_r on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyse the data. The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase (μ*). The apparent dipole moment obtained was μ* = 3.293 D. The effective dipole in the liquid state predicted by the Kirkwood–Frölich theory is 2.530 D. The measured values are compared with density functional and density functional self-consistent calculations (SCIPCM) of the electronic distribution and of the dipole moment of HFC-143a. Finally, the values of the isobaric thermal expansion and isothermal compressibility were estimated from the reported measurements.     

Influence of the chemical composition and comonomer distribution on the dipole moments of 3,3-dimethyloxetane/tetrahydrofuran copolymers

Experimental values of the dipole moment ratio 〈μ₂〉/nm² and its temperature coefficient d ln 〈μ₂〉²/dT, where 〈μ₂〉 is the mean-square dipole moment of a chain with n skeletal bonds and m² is the mean square of the skeletal bond dipole moments, are reported for well-characterized random copolymers of 3,3-dimethyloxetane and tetrahydrofuran. The results are interpreted in terms of the rotational isomeric state theory in a manner consistent with that developed for the parent homopolymers. The theory gives a good account of the experimental results corresponding to copolymers in which the mole fraction of tetrahydrofuran lies in the range 0.11–0.89. It is found that whenever the copolymerization obeys Bernouillan statistics, the dipole moments are quite insensitive to the comonomer distribution. The theoretical analysis suggests, however, that the value of the dipole moment ratio of alternating copolymers of 3,3-dimethyloxetane and tetrehydrofuran should be near that of the parent homopolymer of lower polarity.     

Electronic structure with a dipole moment calculation of the low-lying electronic states of the KHe molecule

The KHe molecular system is extensively studied by multi-reference configuration interaction calculations. Potential energy curves are constructed for 20 lowest electronic states, and molecular parameters are extracted. A comparison of our results with previous works shows remarkable agreement. A further calculation of the dipole moment functions through a wide range of the internuclear separation is performed and their corresponding curves are presented. Charge transfer is detected from the change in the sign of these functions particularly for R < R _e. Negative dipole moment values near R _e are predicted for 3 excited states, (1)²Π, (3)²Σ⁺ and (1)⁴Π, which are of a relatively short-range strong-binding nature. On the other hand, weakly binding long-range excited states predict positive values of the dipole moment near R _e reflecting the K^–He⁺ polarity.     

聚丙烯酸烷基酯侧基差异对链构象性质的影响

针对聚丙烯酸烷基酯侧基形状、极性的不同,基于高分子链的构象-构型统计理论和生成矩阵方法,推出均方电偶极矩和均方回转半径的改进公式,应用于聚丙烯酸甲酯(PMA)链和聚甲基丙烯酸乙酯(PEMA)链等的链构象依赖性质的研究.得到无规PMA4(4态PMA)和PEMA的偶极矩特征比分别为0.63和0.66,温度系数为-0.66×10-3 K-1和1.72×10-3 K-1,无规PMA和PEMA的均方回转半径的特征比分别为1.73和1.43,温度系数为-1.05×10-3 K-1和-1.28×10-3 K-1,均与实验结果符合.而且考虑链规整程度的不同和酯类基团方向等的改变,PMA和PEMA的特征比也呈现较大的差异,尤其对间同构型链PMA4短链,偶极矩及其温度系数均伴有极大值的出现,这些结果表明聚丙烯酸烷基酯侧基对其链构象性质的影响不能忽略.