The microwave spectrum of 14NH3 in the v = 000011 state

The frequencies and assignments of 50 lines in the pure inversion spectrum of ¹⁴NH₃ in the 0001¹ vibrational state are reported in the microwave frequency region 18–53 GHz and in selected regions up to 58 GHz.The J = 0 inversion frequency, K-type doubling constant K, l = 2, ?1 and molecular dipole moment in this state are 32 904.7 ± 2.0 MHz, 1.958 ± 0.040 MHz and 1.459 ± 0.002 D, respectively, where model inadequacies are included in the uncertainties of the first two parameters. The dipole moment measurements for this and the ground state are in excellent agreement with Stark laser measurements. An expression containing the effective l-type doubling constant is obtained from the combination of frequencies $\text{[ν(1, 1, 1) ? ν(1, 1, ?1) ? ν(2, 1, 1) + ν(2, 1, ?1)]}\text{8}\text{= 10 361.894 ± 0.004}\text{MHz}$. A preliminary value for the l-type doubling constant is 10 655 ± 20 MHz.     

NMR of 27 Al in paramagnetic single-crystal DyAl2

NMR of ²⁷Al was observed in a spherical single crystal of DyAl₂ in the paramagnetic state. The well split quadrupole spectrum yielded a quadrupole frequency ν_Q = 561 kHz and hyperfine constant H_hf^p = -3.17 kOe/n_B. The anisotropy of the spectrum is well explained by the dipolar interaction.     

Optical absorption spectrum of the silver dimer ion: temperature dependence measured by photodissociation and photon-trap spectroscopy

The optical absorption spectrum is reported for the silver dimer cation, Ag₂ ⁺, which is temperature-controlled by buffer-gas cooling in an ion trap. The measurement is performed by two methods, photodissociation and photon-trap spectroscopy. The temperature of the trapped ions is estimated from the profiles of the spectrum. The spectrum is further analyzed to evaluate the bond length, r _e , the vibrational frequency, ω _e , and the anharmonic constant, ω _e x _e , in the first excited electronic state based on the molecular parameters reported for the ground state. Absorption and dissociation cross sections are compared as well.     

α-particle preformation for favoured transitions using proximity potential

α-particle preformation probability (P₀) is calculated for favoured transitions of all α-emitters. An indirect approach is employed in which P₀ is given by the ratio of the experimental values of α-decay constant and theoretically determined values of assault frequency and the penetrability. The proximity potential is used for determination of the penetrability, and the assault frequency is calculated through a modified formula. Analysis of the results show that P₀ is highest for the even–even type, and lowest for the odd–odd type α-emitter. Also, it is noted that P₀ is higher for transitions originating in the ground state, and lower for transitions originating in the isomeric state. This suggests that there is greater preformation of α-particle in the ground state than in the isomeric state. P₀ values show a distinct minima at the neutron magic number, N = 126. Also, it is noted that values of α-decay fraction (f_α) reported in the literature for a few α-emitters are, either, not consistent, or only limiting values are available. This raises the possibility of determining improved values of P₀ if accurate values of f_α are known in future.     

Cation self-diffusion in LaFeO3 measured by the solid state reaction method

Cation diffusion in LaFeO₃ has been studied using the solid state reaction between sintered bodies of La₂O₃ and Fe₂O₃ at 950–1350 °C in air or O₂–N₂ mixtures. LaFeO₃ was the only product formed. The growth was parabolic and demonstrated to take place predominantly by diffusion of Fe³⁺ through the LaFeO₃ layer. The self-diffusion coefficient of Fe³⁺ was accordingly calculated from the parabolic rate constant, and at constant activity of La₂O₃, a_La2O3 = 1, it shows Arrhenius-type behaviour with activation energy 320 ± 20 kJ/mol. It appeared to be independent of the surrounding pO₂, but this was ascribed to lack of equilibrium with the atmosphere during growth of the LaFeO₃ layer. Correspondingly, the product LaFeO₃ is probably stoichiometric, and differences between our diffusivity and activation energy and those in the literature are discussed in view of this.     

The large polaron in a magnetic field: Possible existence of a phase transition

It is shown that the ground state energy of a polaron in a magnetic field (calculated in the Feynman approximation) exhibits a discontinuity in the first derivative with respect to α (the electron-phonon coupling constant) if ω_c/ω_o (cyclotron frequency to LO-phonon frequency) is larger than 2.24. This discontinuity has the characteristics of a first order phase transition if α is interpreted as an inverse temperature. For ω_c/ω_o = 2.24 the transition is second order. We found that below the transition point the phonon cloud cannot follow the electron in its motion in the magnetic field.     

Effects of PVA organic binder on electric properties of CaCu3Ti4O12 ceramics

CaCu₃Ti₄O₁₂ ceramics with incorporation of polyvinyl alcohol (PVA) are prepared from the powder synthesized by a solid state reaction. Their electric and dielectric properties are investigated in this study. It is found that adding PVA can dramatically reduce the dielectric loss of CCTO in the low frequency region, and stabilize the dependence of dielectric constant on the measuring frequency. The minimum dielectric loss of 0.045 is obtained from the sample with 8 wt% PVA. The nonlinear coefficient (α) and breakdown electric field (E_b) increase with an increase of PVA binder.     

Temperature dependence of the quadrupole interaction of100Rh in a Cd lattice

The quadrupole interaction frequency |v _q| = |eQV _zz /h|0 = 8.71 ± 0.11 MHz was measured for the 75 keV state of¹⁰⁰Rh in a polycrystalline cadmium matrix by use of the γ-e^? and γ-γ time differential perturbed angular correlation (TDPAC) techniques. The temperature dependence of the electric quadrupole coupling constant for¹⁰⁰Rh in Cd is similar to those of other impurities in Cd metal.     

Synthesis modified structural and dielectric properties of semiconducting zinc ferrospinels

The influence of preparation techniques on structural and dielectric properties of ZnCr_xFe_1−xO₄ (x=0, 0.1 abbreviated as Z and ZC) ferrite nano-particles synthesized using chemical co-precipitation (CCP), sol-gel (SG) and solid state reaction (SS) techniques is discussed. XRD profiles are used to confirm the single phase spinel ferrite formation. TEM images indicate the change in size and shape of particles on changing either the composition or the synthesis methodology. The TEM micrograph of samples obtained through CCP shows uniform particle size formation compared to those obtained through SG and SS. Sample prepared through CCP possess porosity >70% making these materials suitable for sensing applications. The dielectric loss, dielectric constant and ac conductivity are analyzed as a function of frequency, temperature and composition using impedance spectroscopy. A universal dielectric behavior has been predicted through temperature and frequency variations of different parameters. Dielectric constant is found to possess highest value for sample synthesized through SG which marks the possibility of using the SG derived ferrospinels as microwave device components.     

Picosecond measurements of the third order susceptibility tensor in liquids

Single frequency Jamin interferometry is used for observation of non-linear susceptibility tensor measurements in the picosecond range (25 ps). At low density, when avoiding the polarization state instabilities, the displacement of the fringes leads to the measurement of two components of the nonlinear susceptibility tensor. It is shown that X_xyyx (ω = ω + ω - ω) decreases when the pulse duration is reduced, whereas X_{xxxx (ω = ω + ω - ω)} remains constant. This is interpreted by the difference between the orientational and vibrational molecular contributions.     

Magnetic resonance in amorphous FexNi80-xP14B6: I. Ferromagnetic and reentrant alloys

We present a study of ferromagnetic resonance in amorphous Fe_xNi_80-xP₁₄B₆ for Fe concentrations down to that required for ferromagnetism. The resonance was studied at microwave frequencies between 10 and 35 GHz and at temperatures between 2 and 300 K. We find i) in accord with previous data on amorphous ferromagnets, each alloy investigated is magnetically inhomogeneous even in its ferromagnetic state, ii) the intrinsic relaxation parameter λ / Mγ for each alloy falls between the value for pure Fe and the value for pure Ni, iii) a low temperature linewidth rise which is frequency independent and follows an empirical form suggested earlier, iv) frequency dependent linewidth maxima at low T which do not correspond to low field spin freezing temperatures, and v) anisotropy fields intruding at low temperatures. The corresponding anisotropy energy is similar to that proposed for spin glasses as are the temperature and frequency dependences of the anisotropy constant. With part II of this paper, this represents the most complete resonance study to date of the evolution of spin glass behavior in Fe based alloys.     

Dielectric properties of CaCu3Ti4O12–silicone resin composites

CaCu₃Ti₄O₁₂ (CCTO)–silicone resin composites with various CCTO volume fractions were prepared. Relatively high dielectric constant (ε=119) and low loss (tanδ=0.35) of the composites with CCTO volume fraction of 0.9 were observed. Two theoretical models were employed to predict the dielectric constant of these composites; the dielectric constant obtained via the Maxwell–Garnett model was in close agreement with the experimental data. The dielectric constant of CCTO–silicone resin composites showed a weak frequency dependence at the measuring frequency range and the loss tangent apparently decreases with increase in frequency.     

The ν4 state inversion spectra of 15NH3 and 14NH3

The frequencies and assignments of 45 inversion transitions of ¹⁵NH₃ and 15 additional inversion transitions of ¹⁴NH₃ in the ν₄ state are reported. The J = 0 inversion frequency and K-type doubling constant for K,l = 2, ?1 are 31 602.72 MHz and 2.000 MHz for ¹⁵NH₃. The expression containing the effective l-type doubling constant, q₀ - 5q_J - Δη…, is calculated from the (J,K,l) = (1,1,1), (1,1,?1), (2,1,1), and (2,1,?1) transitions as 10 166.022 MHz. The contribution to this expression from the Coriolis coupling with 2ν₂ is estimated for ¹⁴NH₃.     

Donor impurity states in coupled quantum well wires under hydrostatic pressure and applied electric field

In this work we study the binding energy of the ground state for a hydrogenic donor impurity in laterally coupled GaAs/Ga_1−xAl_xAs quantum well wires, considering the simultaneous effects of hydrostatic pressure and applied electric field. We have used a variational method and the effective mass and parabolic band approximations. The low dimensional structure consists of two quantum well wires with rectangular transverse section coupled by a central Ga_1−xAl_xAs barrier. Our results are reported for several sizes of the structure and we have taken into account variations of the impurity position along the growth direction of the heterostructure.     

The assignment of molecular infrared spectra from a laser magnetic resonance spectrometer

Mathematical techniques are presented which have proved useful in assigning the laser magnetic resonance pure-rotation spectrum of HO₂, i.e., useful in assigning an absorption spectrum obtained when molecular energy levels are Zeeman shifted by an external magnetic field until transition frequencies coincide with a fixed-frequency radiation source. The techniques described should have general applicability to the laser magnetic resonance vibration-rotation spectrum of any molecule in an orbitally nondegenerate electronic state and a doublet electronic spin state ($\text{S =}\text{1}\text{2}$). Equations involving both Zeeman line positions and Zeeman line intensities are presented. These allow the assignment of M_J quantum numbers, the determination of the spin-rotation interaction constant γ and rotational quantum number N for both the upper and the lower state, and the determination of the zero-field transition frequency. The equations can be used without prior knowledge of the molecular structure or energy levels.     

Study on the influence of TiO2 on the insulating strength of ZnO-ZnF2-B2O3 glasses by means of dielectric properties

ZnO-ZnF₂-B₂O₃ glasses containing small concentrations of TiO₂ ranging from 0 to 0.6 mol% were prepared. Dielectric properties (constant ε′, loss tan δ, ac conductivity σ_ac over a moderately wide range of frequency and temperature at room temperature in air medium) of these glasses have been studied. The results of these studies were analyzed with the aid of data on optical absorption, ESR and IR spectra of these glasses. The analysis suggests that when the concentration of TiO₂>0.2 mol%, the titanium ions, in addition to Ti⁴⁺ state, co-exist in Ti³⁺ state, act as modifiers and reduce the breakdown strength.     

Mössbauer studies of dilute Au:Er alloys: Obervation of hyperfine structure of ground and excited CEF levels

The hyperfine structure of dilute ¹⁶⁶Er impurities in Au has been investigated between 1.8 and 60 K by Mössbauer spectroscopy. The hyperfine spectrum of the Γ₇ electronic ground state is clearly observed below 4.2 K while at higher temperatures there is an indication of the contribution from the excited CEF-states Γ⁽¹⁾₈ and Γ₆. Using Hirst's relaxation theory for the Γ₇ ground state the magnetic hyperfine coupling constant A=(247±3) MHz and the exchange coupling constant J_sf=(0.10±0.02)eV were derived. A quadruple coupling constant B of about 1 MHz was estimated from the hyperfine pattern of the Γ⁽¹⁾₈ quartet.     

Electric-field-induced energy spectra and dispersions of ZnO/MgxZn1−xO MQWs

The energy spectra and dispersion relations of carriers in the presence of an electric field applied along the growth direction in ZnO/Mg_xZn_1−xO multiple quantum wells (MQW) are calculated using the asymptotic transfer method (ATM) on the basis of the quasistationary state approximation. The energy spectra of the carriers induce some quasi-bound levels under electric fields. The dispersion relations for the energy of the ground state and lower excitation states still have parabolic shapes for both the electrons and the heavy holes in the presence of a moderate electric field. Our results also reveal that the number of energy levels increases with increasing number of ZnO quantum wells and that the energies increase with both increasing Mg composition x and electric field strength.     

Nuclear reactions as an example of the quantum theory of irreversible processes

A modification of the atomic beam magnetic resonance method for investigation of the hyperfine structure of excited atomic states will be described. Radiofrequency transitions between the hyperfine structure niveaus of the excited state, which are unequally populated by circularly polarized light, are detected by observing the resulting change in population number of the hyperfine structure niveaus of the ground state using magnetic deflection in an inhomogeneous field and additional radiofrequency transitions in the ground state as analyzers. As an application the hyperfine structure of the excited 4² P _3/2-state of K³⁹ has been investigated in an almost strong magnetic field of about 65 G with a constant frequency of the applied radiofrequency field of 125.50 Mc/s. The analysis of the radiofrequency signal of the excited state detected as a change in the amplitude of a radiofrequency transition in the ground state yielded the valuesA=(6.10±0.25) Mc/s andB=(1.8±1.2) Mc/s for the hyperfine structure constants of the 4² P _3/2-state of K³⁹. Further possibilities for observing signals of the excited state with the apparatus used in this experiment are also discussed.     

Microwave spectrum,quadrupole coupling constant,and conformation of 1-cyanocyclohexene

The microwave spectrum of 1-cyanocyclohexene has been investigated in the frequency regions 8–12.4 and 18–26.5 GHz. A-Type transitions in the ground state and three excited states have been assigned. The rotational constants in the ground state were determined to be A = 4565.98 ± 0.46, B = 1423.44 ± 0.01, and C = 1136.17 ± 0.01 MHz. From the experimental data, it was suggested that the molecule has an equilibrium half-chair conformation similar to those of cyclohexene and 1-fluorocyclohexene. From the hyperfine splittings of the ¹⁴N nucleus, the quadrupole coupling constant, X_aa, was found to be 4.2 MHz.