Analytical and spectral features of gas-phase chemiluminescence spectrometry of arsenic and antimony

Intense emissions are produced in the u.v. and visible regions when arsine and stibine are introduced into a flow-type furnace—hydrogen diffusion flame system, when the flame is surrounded by oxygen. The emissions in the range 240–300 nm are attributed to AsO and SbO. The emission characteristics seem to be due to chemiluminescence based on the reaction between atomic analyte and oxygen. The detection limits are 0.05 μAs (10 ppb) at 429 nm and 0.1 μ Sb (20 ppb) at 369 nm.     

The characterization of molecular orientation in PVC with emphasis on the use of Raman spectroscopy

A comparison is given of various methods for studying orientation in polymers, with particular reference to PVC. The Raman method and its application to PVC are described in more detail. The results of a study on PVC samples containing 0—20 pph of dioctyl sebacate plasticizer uniaxially drawn at various temperatures in the range 0 to 90°C are summarized. In this work the orientation of the crystalline regions was studied. More recent investigations are briefly discussed in which the orientation of short all-trans noncrystalline syndiotactic segments is investigated and in which Young's modulus of oriented samples is measured for correlation with the Raman data.     

Annihilation electrogenerated chemiluminescence of mixed metal chelates in solution: modulating emission colour by manipulating the energetics

We demonstrate the mixed annihilation electrogenerated chemiluminescence of tris(2,2′-bipyridine)ruthenium(ii) with various cyclometalated iridium(iii) chelates. Compared to mixed ECL systems comprising organic luminophores, the absence of T-route pathways enables effective predictions of the observed ECL based on simple estimations of the exergonicity of the reactions leading to excited state production. Moreover, the multiple, closely spaced reductions and oxidations of the metal chelates provide the ability to finely tune the energetics and therefore the observed emission colour. Distinct emissions from multiple luminophores in the same solution are observed in numerous systems. The relative intensity of these emissions and the overall emission colour are dependent on the particular oxidized and reduced species selected by the applied electrochemical potentials. Finally, these studies offer insights into the importance of electronic factors in the question of whether the reduced or oxidized partner becomes excited in annihilation ECL.     

Heat transfer,development length,and friction factor correlations for the asymptotic region of a laminar arc constrictor

A rigorous equilibrium model is formulated for the laminar flow of plasma through the heating region of a constricted arc plasma generator. The resulting equations are solved for an argon gas using an implicit finite-difference scheme, and the wall shear stress and heat transfer are computed from momentum and energy balances for a wide range of flow rates and arc currents. Friction factors based on this method are in agreement with empirical values to within approximately 10 per cent, and heat transfer calculations agree with the orders of magnitude predicted by a simplified arc model. A dimensionless number peculiar to the constricted arc, the so-called Ohmic heating parameter, is used to correlate the mean Nusselt numbers in the asymptotic arc regime. When the fluid properties are based on the mean temperature, the product of friction factor and Reynolds number is found to be a constant for currents below 200 Amp and to vary with the Ohmic heating parameter for larger currents. Correlations are also presented for the thermal development length, and the agreement with experiment is good.     

Inhibition of the proteolytic activity of anthrax lethal factor by aminoglycosides

The anthrax lethal factor (LF), a Zn-dependent endopeptidase, is considered the dominant virulence factor of anthrax. Because pharmacological inhibition of the catalytic activity of LF is considered a plausible mechanism for preventing the lethality of anthrax, a high-throughput screening experiment based on LF-catalyzed cleavage of a fluorescent substrate was performed to identify novel inhibitors of LF. The RNA-targeting antibiotics, neomycin B and some synthetic dimeric aminoglycosides, were found to be nanomolar active-site inhibitors of LF.     

The effect of sample environment on the room-temperature phosphorescence of several polynuclear aromatic hydrocarbons

Room-temperature phosphorescence (r.t.p.) of numerous molecules has been studied with emphasis on several polynuclear aromatic hydrocarbons (PAH). The heavy atom effect has led to a significant enhancement of r.t.p. signals for the PAH studied with the trend being Tl⁺ > Ag⁺ > Pb²⁺ > Hg²⁺. The Tl⁺ also resulted in enhanced spectral features of emission bands. R.t.p. could be induced from PAH on a sodium acetate sample support as well as on filter paper. A study of the effect of different gaseous environments provided anomalous results.     

Second harmonic generation from alkali metals

Nonlinear optical constants of the alkali metals, responsible for the second harmonic generation, are calculated using the Drude model. It is found that the electric quadrupole term of the nonlinear polarization is larger than that of a previous theory of Jha by a major factor of ω²_p/ω². By considering a more realstic electron density distribution, we also obtain an additional dipole term due to symmetry breakdown at the surface. The new nonlinear polarization gives the reflected second harmonic intensity in good agreement with experiments.