Frequency dependence of the large,electronic χ(3) in polyacetylene

The third order optical susceptibilities (χ⁽³⁾) of trans- and cis- (CH)_x have been determined in the spectral region below the gap by measuring the third harmonic generation efficiency. The magnitude of χ⁽³⁾ parallel to the polymer chains in trans-(CH)_x is in excess of 10⁻⁹ esu for wavelengths larger than 1.3 μm, and the spectrum of χ⁽³⁾ in trans-(CH)_x has a sharp two-photon resonance at an energy corresponding to half the semiconducting gap. Both the off resonance and the two-phonon resonance enhanced values of χ⁽³⁾ are explained by a simple band picture.     

Non-existence of long-range order in a model of polyacetylene

Polyacetylene (CH)_χ, a one-dimensional polymer, is studied as a model of quantum statistical mechanics. The effective Gibbs measure of phonons in (CH)_χ is obtained by integrating out the fermion degrees of freedom, and it is shown that the effective interactions of phonons are rather complicated many-body ones but of short range (at least for small coupling constant g or for small inverse temperature β). Thus the Araki-Ruelle theory implies non-existence of long-range orders in this system.     

Electrical transport in electron beam irradiated polyacetylene

Electrical conductivity of non-doped (CH)_x decreases a little and its activation energy increases a little by the electron beam irradiation. The increase of the electrical conductivity of the irradiated (CH)_x by I₂ doping is not so remarkable compared with that of non-irradiated (CH)_x. The conductivity of heavily irradiated (CH)_x is very low even after halogen dopings.On the other hand, the effect of the electron beam irradiation on the conductivity of previously I₂ doped (CH)_x is much less compared with that doped after the electron beam irradiation. These results are explained tentatively by the role of I₂ molecules in the initial stage of radiolysis and the suppression of the cross-linking.     

Paramagnetic susceptibilities, crystal field Stark energies and hyperfine properties of Eu in europium trifluoromethanesulfonate nonahydrate

Hexagonal single crystals of europium trifluoromethanesulfonate nonahydrate (EuTFMS) have been prepared. The paramagnetic susceptibility perpendicular to the symmetry axis (c-axis, χ_⊥) and the principal magnetic anisotropy (Δχ=χ_||−χ_⊥) were measured in the temperature range of 300-13 and 300-80 K, respectively. The paramagnetic susceptibility parallel to the c-axis (χ_||) was calculated using the values of χ_⊥ and Δχ. χ_|| and χ_⊥ increase slowly with decrease of temperature and below ∼93 K, χ_⊥ is more or less constant. But χ_|| levels off below ∼137 K. The calculated value of the effective magnetic moment (P_eff) of Eu³⁺ in the crystalline environment of EuTFMS decreases with lowering of temperature. The Raman and Fourier transform infrared (FTIR) spectra of EuTFMS were recorded in the wavenumber range of 10-1800 and 370-6000 cm⁻¹, respectively. A good theoretical simulation of the observed magnetic properties including the CF Stark energies of the ground term (⁷F) extracted from the Raman and FTIR spectra of Eu³⁺ in EuTFMS have been achieved using one electron crystal field (CF) analysis. The electronic specific heat and other relevant CF dependent hyperfine properties, viz, nuclear quadrupole splitting and hyperfine specific heat have been computed.     

Chemiluminescent emission of CH*, C*<Subscript>2</Subscript>, OH*, and CO*<Subscript>2</Subscript> during the ignition of ethane behind reflected shock waves

The chemiluminescent emission from CH*, C*₂, OH*, and CO*₂ during the self-ignition of various mixtures of ethane with oxygen and argon behind reflected shock waves in the 1240–1790 K temperature range at a total concentration of the mixture М ₅ = (1 ± 0.2) × 10^?5 mol/cm³ is experimentally studied. It has been shown that the time-to-maximum in the emission intensity profiles is almost identical for all the emitters studied. How the pattern of the OH* emission profile changes with the temperature and mixture composition is examined. The CH* and C*₂ emission profiles demonstrate virtually symbatic behavior in the covered ranges of temperature, pressure, and equivalence ratio. It is established that the emission signals from OH* and CO*₂ appear earlier than the C*₂ and CH* emission signals. The numerical simulation predictions are found to be in close agreement with the experimental results.     

Infrared superbroadband emission of Bi ion doped germanium-aluminum-sodium glass

The 96GeO-(3-χ)Al₂O₃-χNa₂O-1NaBiO₃ (χ = 0, 0.5, 1.5 molar percent designated as A1, A2 and A3) and 96GeO-(3.5-ψ)Al₂O₃-ψNa₂O-0.5Bi₂O₃ (ψ = 0.5, 1, 2 molar percent designated as B1, B2 and B3) glasses were prepared by conventional melting method with the measurement of their DTA curve, fluorescence decay curve, transmission, absorption and emission spectra. The near infrared superbroadband emission characteristics of the A1, A2, B1 and B2 glasses peak at ∼1220 nm were observed when pumped by an 800 nm laser diode. The stimulated emission cross section (σ_p) was obtained from the emission spectra. The result indicated that the introduction of Bi⁵⁺ in NaBiO₃ into raw materials could increase the emission intensity of the obtained glasses by 5.6 times than that of Bi³⁺ in Bi₂O₃, and the FWHM (Δλ) and emission lifetime (τ) at 1220 nm increased from 195 nm to 275 nm, and 280 μs to 434 μs. Meanwhile, it was found that the absorption edges were blue-shifted from 486 to 447 nm by comparing those of A1 and B1. The absorption edges were considered to be ascribed to the charge transfer from Bi³⁺ 6s² to Bi⁵⁺ 6s⁰. Therefore we could conclude that the content of Bi⁵⁺ ions in A1 was more than that in B1 glasses. It could be deduced from the emission and absorption spectra that the stronger emission intensity and wider FWHM were due to the higher concentration of Bi⁵⁺ ion in glass. In particular, the increase of Na₂O content was in proportion to the thermal stability and the value of σ_p × τ and σ_p × Δλ of glasses.     

K→ππγ and chiral perturbation theory

Weak radiative decaysK _L,S →π⁺π^?γ andK ⁺→π⁺π⁰γ are reexamined. The electromagnetic form factors and long-distance contributions to the direct photon emission are evaluated using the higher order effective chiral Lagrangian. We find that (1) the naive soft-pion theorem cannot be applied to the magnetic-type transition amplitude, (2) the shortdistance contribution toK _L →π⁺π^?γ is comparable to or even bigger than the long-distance one, (3) the ΔI=1/2 enhancement persists in the decayK ⁺→π⁺π⁰γ, (4) to the order of 1/Λ _χ ² (Λ _χ being the chiral-symmetry breaking scale) the direct photon emission amplitude does not receive a contribution from penguin operators, and (5) the 1/N _c expansion improves the discrepancy between theory and experiment.     

Particle effects on the emissivity and temperature of optically thick, mixed media retrieved by mid-IR emission spectroscopy

Passive diagnostics offer new ways of obtaining real-time data for the control and modeling of industrial furnaces. It has been proposed elsewhere that from the intensity profile between 3.8 and 4.7 μm one may derive the temperature of a gas-particle medium and the particle emissivity (ε_p) at 3.95 μm. This technique applies to large columns of combustion products with enough CO₂. The temperature is retrieved by finding the best fit between Planck's function and the intensity profile between 4.56 and 4.7 μm, which is that of a blackbody due to CO₂ saturation. Here we consider the effect of particles on the intensity profile and, therefore, on the retrieved temperature and particle emissivity. We derive an analytic approximation of the effective emissivity for an optically thick gas-particle mixture that includes emission and absorption due to particles and gases, along with isotropic particle scattering. The derivation follows the method of embedded invariance and has been used already for particle-only clouds. It yields a spectral solution that is applicable in other infrared regions where gas and particle optical thicknesses are large. A key parameter (χ) is the ratio of the gas absorption coefficient to the particle extinction coefficient. For χ=1 and ε_p=0.5, particle effects decrease the gas band profile by 5% from that of a blackbody. For χ<1 and ε_p<0.5, particle effects on the calculated temperature and particle emissivity are noticeable and particle effects should be considered. If χ is known, an iterative procedure may be used to calculate temperature and particle emissivity. We illustrate this procedure with data from a coal-fired boiler. Accounting for particle effects, temperatures were 4% higher (at about 1500 K) and particle emissivities 28% lower (for ε_p within 0.3-05) than without considering these effects.     

Superconductivity in the pseudo-binary A-15 compounds Mo3Os1−χRuχ and Mo3Ir1−χRuχ

Superconducting transition temperatures (T_c) and room temperature lattice parameters (α_o) are reported for the A-15 pseudo-binary systems Mo₃Ir_1−χRu_χ and Mo₃Os_1−χRu_χ (0 ≤ x ≤ 0.8). If Mo₃Ru could be synthesized in the A-15 structure, its T_c and α_o are predicted to be 10–11°K and 4.95 Å, respectively.     

Doping effect on photoluminescence of polyacetylene

Luminescence peaks of both cis-and trans-(CH)x shift to lower energy and their intensities decrease with decreasing temperature. On the other hand, the luminescence peak of cis-(CH)x shifts to higher energy and its intensity decreases with I₂ doping into (CH)x. These results are discussed, tentatively, in terms of luminescence originated from self localized state in (CH)x.     

What is measured in a time-resolved stimulated Raman experiment?

We have performed four-beam time-resolved stimulated Raman measurements on liquid CS₂. To interpret our results we have applied the response formalism for the third-order polarization to such an experiment. It turns out that the measured quantity is proportional to (a convolution of) Abs[χ⁽³⁾(-ω_s, ω_s, ω_l, -ω_l)]. As a consequence in this four-beam e xperiment one picks up electronic contributions in contrast to a two-beam experiment where Im[χ⁽³⁾] is observed.     

Phase transitions in Fe doped VO2

Resistivity measurements were performed on single crystals of V_1-χFe_χO₂ (0 ? χ < 0.03). Anomalies in the ln σ vs T^-1 curve indicate the presence of different structural phases. The results of these experiments and previous ⁵⁷Fe Mössbauer data are discussed in terms of a model recently proposed by Pouget et al. for the structural phases in the system V_1-χCr_χO₂     

Emission bands of AIH (X1Σ+): The 2-0 sequence

Seven bands of the 2-0 sequence of AlH in its X¹Σ⁺ ground state have been observed in emission from a carbon furnace and recorded with a Bomem interferometer. Improved values for the molecular constants have been obtained. The principal constants are B_e = 6.3937(4), α₃ = 0.1868(3), 10⁴D_e = 3.683(10), ω_e = 1682.43, and ω_eχ_e = 29.11 cm⁻¹, where the error limits are 3σ. Possibilities for observing AlH in astrophysical sources are discussed.     

Phototransport effects in polyacetylene, (CH)x

We have made the first comprehensive measurements of the photovoltaic and photoconductivity effects in polyacetylene in that we have extended the spectral range originally covered by Matsui and Nakamura [17] to include the visible region as well. The photovoltaic experiments were done on Schottky barrier junctions formed between AsF₅ lightly-doped p-type trans-(CH)_x and a low work function metal, the first junctions of this type to be produced in semiconducting polyacetylene. The observation of a photovoltaic response threshold at 1.48 eV provides the first definitive measurement of the single-particle band gap in trans-(CH)_x. In addition, we have found the existence of a peak at 1.35 eV in the photoconductivity spectrum of undoped trans-(CH)_x which may be due either to extrinsic sources or to thermal dissociation of a weakly bound Wannier exciton.     

Systematic trends in the transport mean free path with electron energy and atomic number

The inelastic mean free path, λ_i, and the transport mean free path, λ_tr, hold the key to understanding the effects of elastic scattering of electrons in electron spectroscopy techniques such as Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Systematic trends in the variation of λ_tr and χ=λ_i/λ_tr with atomic number, Z, and electron energy, E, are explored using the differential elastic scattering cross-section data of Czyzewski et al. (J. Appl. Phys., 68 (1990) 3066). At low Z, λ_tr increases with energy in accord with the predictions of the Born approximation, but at higher Z, a more complex behaviour is revealed. In the first and second transition metal series, χ varies little with energy over much of the kinetic energy range probed in XPS in accord with the energy scaling ideas from the semi-classical scattering theory of Tilinin (Soviet Physics JETP, 67 (1992) 1570). In the third transition series, a pronounced minimum is found at around 200 eV, with χ for Au lower than for the corresponding transition metals. The results identify regions of the periodic table where elastic scattering effects are particularly pronounced.     

Measurements of magnetic susceptibilities,their anisotropies and crystal field investigations of monoclinic single crystals of Ho2GeO5

Monoclinic single crystals of Ho₂GeO₅ were grown by a flux technique. The molar principal susceptibilities (χ₁ and χ₃) have been measured in the temperature range 300–13.5 K. The principal magnetic anisotropies (χ₁–χ_2,χ₂–χ₃ and χ₁–χ₃) are obtained from the measured anisotropies in different modes of suspensions (b-axis vertical, c-axis vertical and (1 0 0) plane horizontal) of the crystal. The molar principal susceptibility (χ₂) is obtained from the observed values of the principal anisotropies. The observed principal susceptibilities together with their anisotropies are explained by invoking the crystal field interaction of the Ho³⁺ ion with its diamagnetic neighbors in non-axial symmetry. The molar susceptibilities are correlated to the ionic values by finding out the proper orientation of the principal molar susceptibilities, i.e., crystal susceptibilities with respect to that of the ionic susceptibilities (K_x, K_y and K_z). The electronic heat capacities are calculated from the crystal field analysis showing Schottky type anomalies.     

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.     

Solitons and solar cells: The non-equilibrium thermodynamics of the photovoltaic effect in polyacetylene

The production of photovoltages by trans-(CH)_x based devices is analyzed in terms of the non-equilibrium thermodynamics of the photovoltaic effect and compared with the model of photogenerated charged soliton pairs. It is concluded that the source of (CH)_x photovoltages is a photo-reaction channel in which photoexcitations remain as band electrons and holes for appreciable lifetimes.     

Proton NMR studies of the structure of trans-(CH)x

The proton NMR line width in undoped and AsF₅ doped polyacetylene shows an abrupt change as a function of temperature, indicative of motional narrowing. The characteristic temperature for the onset of narrowing decreases with increasing AsF₅ concentration. The results are discussed in terms of large amplitude librational or translational motions of the trans-(CH)_x chains. The magnitudes obtained for the second moment at temperatures below and above the narrowing transition are used to obtain information on the chain packing of trans-(CH)_x within the three-dimensional crystal structure.     

The millimeter wave rotational spectrum of N-cyanomethanimine,CH2NCN

The rotational spectrum of the short-lived species N-cyanomethanimine, CH₂NCN, has been measured in the frequency range 100–250 GHz. The observed transitions allow the determination of the rotational and centrifugal distortion constants and the nitrogen quadrupole coupling constants for both nitrogen nuclei. The N-cyanomethanimine spectrum was measured directly in the products of the pyrolysis of trimethylenetetrazole. The rotational constants obtained are A = 63 372.995(11) MHz, B = 5 449.347 90(28) MHz, and C = 5 009.559 86(29) MHz; the quadrupole coupling constants are χ_aa = 2.057(39) MHz and χ_bb ? χ_cc = ?7.205(21) MHz for the imine nitrogen, and χ_aa = ?3.264(33) MHz and χ_bb ? χ_cc = ?1.630(18) MHz for the cyano-group nitrogen. The accurate constants obtained allow the calculation of the line position and hyperfine structure of any rotational transition appropriate for a radioastronomical search.