Determination of the kinetic parameters of the isomerization reaction of ethyl isocyanide using HeI photoelectron spectroscopy

The use of HeI photoelectron spectroscopy (PES) for the kinetic study of chemical reactions was introduced previously by us. As another example of the determination of the kinetic parameters of a chemical reaction using the PES method, the isomerization reaction of ethyl isocyanide CH₃CH₂NC → CH₃CH₂CN is investigated. It is found to be first order and the kinetic equations at 193.6, 200.0 and 210.3°C can be expressed as ln R_{466.6 K} = − (7.600 ± 0.026) × 10⁻⁵t − 0.4350; ln R_{473.0 K} = − (1.329 ± 0.032) × 10⁻⁴ − 0.4375 and ln R_{483.3 K} = − (3.170 ± 0.052) × 10⁻⁴ − 0.4354, respectively. The rate constants of the reactions at 193.6, 200.0 reactions at 193.6, 200.0 and 210.3°C are respectively (7.600 ± 0.026) × 10⁻⁵, (1.329 ± 0.032) × 10⁻⁴ and (3.170 ± 0.052) × 10⁻⁴ s⁻¹. The calculated activation energy (E_a) of this isomerization reaction is 38.36 ± 0.32 kcal mol⁻¹. These results are also in excellent agreement with the results obtained by a traditional method. This means that PES is a valuable method for determining the kinetic parameters of chemical reactions. The value of the intercept in the kinetic equations is related to the logarithm of the ratio of the photoionization cross-section of the bands used. This also means that the relative photoionization cross-sections of the bands used for the sample studied are obtained in the kinetic study of a chemical reaction using the PES method.     

Thermal dependence of conduction properties in the Bi2O3Pb2OF2 system

Conduction properties of bismuth-lead oxyfluorides (Bi,Pb)₂(O,F)₃ have been investigated by complex impedance analysis. A special attention has been drawn to a hexagonal solid solution Bi_(1−x)Pb_xO_(1.5−x)F_x (0.45⩽x⩽0.741 at 770 K), which is isostructural with ALa₂O₃. Conductivity values range from 3 × 10⁻⁵ to 3 × 10⁻² (ω cm)⁻¹ at 585 K. A minimum associated with a maximum in activation energy is observed for the composition x = 0.5 i.e. BiPbO₂F.     

The high-resolution spectrum of the ν1 (A1) band of 12CD3F

The spectrum of the ν₁ (A₁) band of ¹²CD₃F has been recorded with a resolution of 0.010 cm⁻¹ and deconvolved to 0.005 cm⁻¹. Over 1050 transitions have been assigned with K ≤ 16 and J ≤ 42. The spectrum is highly perturbed, exhibiting avoided crossings in most of the observed sub-bands. The origin of most of the local and global resonances has been determined and the coupling constants estimated. Due to the complexity of the spectrum resulting from the 24 potential interacting states in the region, the assigned frequencies were fitted in a restricted manner (K ≤ 3, J ≤ 15), to obtain the following effective constants for the band: ν₀ = 2090.8118(20) cm⁻¹, α^A = 1.19743 × 10⁻² cm⁻¹, and α^B = −1.8489 × 10⁻³ cm⁻¹. From an unrestricted least-squares analysis, fixing the above parameters the β's (D_v^x = D₀^x − β_v^x) were calculated to be β^J = 1.7776 × 10⁻⁷ cm⁻¹, β^JK = 8.3406 × 10⁻⁷ cm⁻¹, and β^K = −6.3829 × 10⁻⁷ cm⁻¹. These constants serve as good starting parameters for the global analysis necessary to fully analyze the 5-μm region of the ¹²CD₃F spectrum.     

Type III - Type I transition and strain-effect in Hg1−xCdxTeCdTe and Hg1−xZnxTeCdTe superlattices

In this paper, the results of Hg_1−xZn_xTeCdTe strained layer superlattices grown by MBE are reported, and compared to Hg_1−xCd_xTeCdTe superlattices. Both Type III and Type I Hg_1−xZn_xTeCdTe superlattices with different strain have been grown on CdTe(111)B/GaAs(100) and CdTe(100)/GaAs(100) substrates and characterized by electron, X-ray diffraction, infrared transmission and Hall measurements. The values of hole mobility between 5×10³ up to 2×10⁴cm²v⁻¹s⁻¹ at T = 23K along (111)B growth orientation and up to 4.9×10⁴cm²v⁻¹s⁻¹ at T = 5K along (100) growth orientation are obtained for Type III superlattices whereas in Type I superlattices, the hole mobility is between 200–300cm²v⁻¹s⁻¹. This drastic change in the hole mobility between Type III and Type I superlattices along with the role of the strain are discussed in this paper.     

Synthesis and ionic conduction of C3A-type nasicon Na3+3x−yY1−xSi3−yPyO9

In the solid solutions of Na_3+3x−yY_1−xSi_3−yP_yO₉, new fast Na⁺ -conductors were obtained. The ionic conductivity, σ, and the activation energy, E, of the most conductive material, Na_4.425Y_0.375Si_2.55P_0.45O₉ were 5 × 10⁻³ S/cm at 300°C and 10 kcal/mol, respectively. Those values were strongly dependent upon the composition. With an increase of Na concentration, [Na], σ increased and E decreased. Accommodation of higher [Na] in the structure was madefeasible by decreasing [Y] and increasing [P]. Based on the crystal structure assumed for Na_3+3x−yY_1−xSi_3−yP_yO₉ and on the above results, a conduction model was presented. The structural consideration revealed that a conduction path is formed along the 〈1 1 1 〉 direction, where Y³⁺ ions locate in the way of Na⁺ ions.     

Dipole co-operative motions in an A-type carbonated apatite,Sr10(AsO4)6CO3

Relaxation of reorientable electric dipoles in A -type carbonated strontium arsenate, an apatite, has been studied with the thermally stimulated currents method. The fractional polarization technique permitted registration, in the range 9–428 K, of a separate current vs temperature curve for each small range of dipole-reorientation activation energies. Interpretation of these on a simple Debye model revealed four compensation temperatures, −100, 175, 392 and 573°C, with associated relaxation times τ_c = 2 × 10⁻⁶, 9 × 10⁻⁷, 2 × 10⁻⁶, and 1 × 10⁻⁵s, respectively. It is proposed that (1) the reorientable dipoles are primarily carbonate ions, and that (2) the co-operative phenomena associated with the 175°C and 392dgC temperatures are, respectively, a quasi-statically stabilized monoclinic-to-hexagonal phase transition and the onset of dynamical stabilization of the hexagonal phase.     

On W±, Z0, γ self-interactions: High energy behaviour and tree unitarity bounds

We analyze the high-energy behaviour of vector boson scattering amplitudes within the framework of a recently suggested lagrangian model based on global weak isospin symmetry broken by electromagnetism. Requiring vanishing of the most strongly (as s²) rising contribution to vector boson scattering amplitudes leads to vector boson self-interactions dependent on a single parameter, for which the anomalous W^± magnetic moment, κ, can be chosen. Tree unitarity is violated at about 2 TeV for arbitrary κ as in the SU(2)_L × U(1)_Y theory for m_H → ∞. The model is well suited for significant tests of the vector boson sector of the SU(2)_L × U(1)_Y electroweak theory in processes such as e⁺e⁻ → W⁺W⁻.     

Ionic conductivity and crystal structure for the Li3−2xCr2−xTax(PO4)3 system

The monoclinic phase (P2₁/n) was formed for 0≤x≤0.6 and the NASICON-type rhombohedral phase (R3̄c) was obtained for the region 0.8≤x≤1.2 in the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The activation energy for Li⁺ migration was ca. 0.45 eV for the monoclinic structure and ca. 0.36 eV for the rhombohedral structure. The maximum conductivity of 8.4×10⁻⁶ S cm⁻¹ at 298 K was obtained for x=0.8 of the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The conductivity of LiCrTa(PO₄)₃ was enhanced about three to five times by the addition of the lithium salt due to the improvement of the sinterablity. The maximum conductivity was 2.4×10⁻⁵ S cm⁻¹ at 298 K for LiCrTa(PO₄)₃–0.2Li₃BO₃.     

Determination of A0 for CH3D from perturbation-allowed transitions

Ground state combination differences obtained from normally allowed and perturbation-allowed transition in the 2ν₆ band of ¹²CH₃D have been fitted to obtain the following values for rotational constants: A₀ = 5.2508231 ± 0.0000043 cm⁻¹, and D₀^K = (−7.869 ± 0.23) × 10⁻⁵cm⁻¹.     

Observation of RF superconductivity in Y1Ba2Cu3O9−δ AT 3 GHz

Two samples of Y₁Ba₂Cu₃O_9−δ, one fabricated at Los Alamos National Laboratory and the other at the University of Wuppertal, were tested in the rf field of a niobium cavity at 3 GHz and in a temperature range from 4.2 to 300 K. The data show a sharp reduction of the Joule losses in the samples beginning at an onset temperature of 98 and 92 K, respectively. The residual losses of the sample were measured at 4.2 K where the host cavity was superconducting. The ratio of these losses to the ones observed slightly above T_c was less than 1.1 × 10⁻². This indicates that only a small fraction of the conduction electrons of the Y₁Ba₂Cu₃O_9-δ sample remain unpaired. The dependence of the rf losses on the rf magnetic field allows the determination of a maximum surface current density which is found to be about 5 × 10⁴ A/cm².     

Anionic conductivity and thermal stability of single crystals of solid solutions based on calcium fluoride

The temperature and composition dependencies of the anionic conductivity in the temperature range from ambient to 1073 K were studied for single crystals of Ca_1−xGd_xF_2+x (x=1×10⁻⁴, 1×10⁻³, 1×10⁻² and 1×10⁻¹) and of Ca_0.8R_0.2F_2.2 (R=La, Ce, Pr, Nd, Gd, Dy, Er, Tm, Yb, Lu and Y), having the fluorite structure. The conductivity plots for the concentrated Ca_0.8R_0.2F_2.2 solid solutions display the low-temperature and high-temperature linear (Arrhenius) regions with the knee temperature T_k∼770 K. The values of the conductivity activation enthalpy obey the relation ΔH_HT(T>T_k)>ΔH_LT(T<T_k). The conductivity mechanism in heavily doped Ca_1−xR_xF_2+x crystals is associated with the clusters of the point defects which decrease the potential barriers for fluoride anions moving by hops over the structural sites of the anion sub-lattice. We studied the effect of the dimensional factor (doped cation radii) on the anionic transport in these crystals. A correlation between anionic transport and atomic structure of the studied crystals is discussed.     

ESR study of vanadyl ion in tripotassium citrate

ESR spectra of VO²⁺ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 2.001 ± 0.001, g_y = 1.997 ± 0.001, g_z = 1.945 ± 0.001, A_x = (49.0 ± 1) × 10⁻⁴ cm⁻¹, A_y = (66.8 ± 1) × 10⁻⁴ cm⁻¹ and A_z = (168.4 ± 1) × 10⁻⁴ cm⁻¹. The covalency and Fermi contact terms are evaluated and compared with those of other lattices.     

Pattern of E6 symmetry breaking in the superstring theory

A mechanism of symmetry breaking by the Wilson loop is discussed. In particular, we take the Wilson loop to break the E₆ symmetry of superstring theory down to SU(6)×U(1)_T3R and then to SU(3)_L×U(1)_Y in succession. By the fine tuning parameters we obtain sin²θ_W=0.215, the proton life time τ_p≈10³⁴yr and the two intermediate mass scales M_I≈10¹⁶⁻¹⁷ GeV and M_II≈10⁵⁻¹⁰ GeV.     

Synthesis and electrical transport properties of Lu2+xTi2−xO7−x/2 oxide-ion conductors

The Lu_2+xTi_2−xO_7−x/2 (x = 0; 0.052; 0.096; 0.286; 0.44; 0.63; 33.3–49 mol% Lu₂O₃) nanoceramics with partly disordered pyrochlore-type structure are prepared by sintering freeze-dried powders obtained by a co-precipitation technique with 1600 °C annealing. Similar to pyrochlore-like compositions in the zirconate system, some of the new titanates are good oxide-ion conductors in air. The new solid-state electrolytes have oxide-ion conductivity in the interval of 1.0 × 10^− 3 – 2.5 × 10^− 3 S/cm at 740 °C in air. This value of conductivity is comparable with that of ZrO₂/Y₂O₃ ceramics. The conductivity of Lu_2+xTi_2−xO_7−x/2 depends on the chemical composition. The highest ionic conductivity is exhibited by nearly stoichiometric Lu_2+xTi_2−xO_7−x/2 (x = 0.096; 35.5 mol% Lu₂O₃) material containing ∼ 4.8 at.% Lu_Ti anti-site defects.     

Microwave spectrum,conformation, and quadrupole coupling constants of 1-iodopropane

The molecular rotational spectrum of 1-iodopropane (n-propyl iodide) has been investigated in the frequency region 9–33 GHz. The 1-iodopropane molecule has been confirmed to exist in two rotational isomers, trans and gauche. The rotational constants of the ground state were determined to be A = 10 595.450(60) MHz, B = 1781.669(8) MHz, and C = 1614.200(7) MHz for gauche, and B = 1305.247(8) MHz and C = 1269.365(7) MHz for trans. The nuclear quadrupole coupling constants were determined to be χ_aa = −1020(3) MHz, χ_bb = 193(2) MHz, χ_cc = 827(4) MHz, χ_ab = 1173(2) MHz, χ_ac = −369(7) MHz, and χ_bc = 230(5) MHz for gauche, and χ_aa = −1509(8) MHz, χ_bb = 610(9) MHz, χ_cc = 899(12) MHz, and χ_ab = −789(9) MHz for trans. The centrifugal distortion constants were also determined using all of the assigned transitions. From the relative intensity measurements the skeletal torsional frequencies for the gauche and trans forms were estimated to be 117 and 108 cm⁻¹, respectively.     

Diffusion of Fe,Co, Nd,and Dy in R2(Fe1−xCox)14B where R=Nd or Dy

Transition metal and rare earth diffusion coefficients at 1323 K in Dy_2−yNd_y(Fe_1−xCo_x)₁₄B were determined by field emission energy dispersive spectroscopy compositional analysis of diffusion couple specimens. Various arrangements of component materials and temperatures were examined in order to understand the mechanisms affecting diffusion of the components and to predict the stability of functionally graded microstructures consisting of a dysprosium-rich (Dy_2−yNd_y(Fe_1−xCo_x)₁₄B) outer layer and a neodymium-rich (Nd₂(Fe_1−xCo_x)₁₄B) interior. Estimates of the mutual interdiffusion coefficients of Dy, Nd, Fe, and Co in this system were obtained from the preparation of arc melted and annealed polycrystalline specimens, assuming that the diffusion coefficients were independent of concentration (Grube solution). Fifteen diffusion couples were prepared and heat treated at 1323 K for various times in order to provide data for calculation of the diffusion coefficients. The results indicate that the diffusion coefficients of Fe and Co (D_Fe=3.28×10⁻¹⁰ cm²/s and D_Co=7.63×10⁻¹⁰ cm²/s) were significantly higher at 1323 K in this system than those for Dy and Nd (D_Nd=2.3×10⁻¹² cm²/s and D_Dy=2.9×10⁻¹² cm²/s).     

Millimeter-wave spectrum of the C4v molecule IOF5: l-type doubling of the kl = −1 transitions in the v11(E) = 1 state spectrum

Measurements of the rotational spectrum of the C_4v molecule IOF₅ are reported for the excited vibrational state v₁₁(E) = 1 for the transitions J13 ← 12, 14 ← 13, 16 ← 15, and 17 ← 16 (55–72 GHz) including the observation of the kl = −1 (q⁻), l-doubling effect. Detailed assignments of the E-state spectrum are presented based on the overlapping quadrupole structure. These data are analyzed together with earlier results for the excited vibrational state v₆(B₁) = 1 to give information concerning the ν₆(B₁)-ν₁₁(E) Coriolis interaction and the (Δl, Δk) = (2, 2) (q⁺) and (2, −2) (q⁻)l-resonance interactions. It is found that q₁₁⁻ = −2.57(10) MHz, |q₁₁⁺| = 0.094(20) MHz, Δ = ν₆ − ν₁₁ = 45.2(7) cm⁻, ζ_11,11^z = +0.18(1) and |ζ_6,11^y| = 0.73(4).     

Spectroscopy of the excited C-O stretching Q branch of 13CD3OH: Measurement and assignment of new FIR laser lines

The Q branch of the C-O stretching fundamental band of ¹³CD₃OH has been investigated. Starting from a high resolution (4 × 10⁻³cm⁻¹) infrared Fourier transform spectrum and using a waveguide CO₂ laser of 300 MHz tunability and an acoustooptic modulator for an extension of ±90 MHz, 31 new FIR laser lines have been observed. The related absorptions have been measured by means of optoacoustic detection. The frequency of one new FIR laser line was also measured. Eight tentative assignments are proposed for the IR absorption and FIR laser emissions.     

Oxygen diffusion in YBa2Cu3O7−x; An impedance spectroscopy study

The ionic conductivity of YBa₂Cu₃O_7−x has been studied in the temperature range of 650 to 1085 K, using Pt(O_z)/YSZ electrodes, which are ionically reversible, and blocking for electronic charge carriers. A.c. and d.c. polarization studies in air reveal an ionic conductivity activation enthalpy of 1.51 eV. In the range of 775 to 890 K ionic transference numbers range from 2×10⁻⁷ to 8×10⁻⁸. The enthalpy value is related to ionic conduction via oxide ion vacancies V_Ö, and oxygen loss.