Crystallization impedance in the case of D.C. superposition

An expression for the impedance frequency dependence in the case of d.c. superposition has been derived and analyzed for the crystallization process of metals taking into account the two-dimensional diffusion of ions in solution and the surface diffusion of adatoms and using the simplest surface model with parallel step lines. It is shown that in the general case it is impossible to present the crystallization impedance as the sum of the surface diffusion impedance and the Warburg impedance. It has been found that in the case of anode polarization an unusual effect of the impedance increasing with agitation intensity takes place which is typical of this mechanism. Possible methods for determination of the model parameters from impedance measurements are discussed. The authors suggest an iteration procedure which permits to determine all the parameters of the model under consideration including the surface diffusion coefficient of adatoms and the spacing between the growth step lines.     

Microstructure determination of poly-(1,3-pentadiene) by a combination of infrared, 60-MHz NMR, 300-MHz NMR,and X-ray diffraction spectroscopy

A quantitative procedure has been developed for characterizing the complete microstructure of polymers of 1,3-pentadiene, including the tacticity of any crystalline component. This can be accomplished by a combination of infrared spectroscopy, X-ray crystallinity, and 300-MHz NMR spectroscopy. A series of high structural purity polymers were synthesized with a series of previously unreported mixed microstructures. These samples were characterized by using the three techniques mentioned, including the previously unreported 300-MHz NMR data. With those results a 60-MHz NMR/IR method of spectroscopy was developed to determine the composition of poly(1,3-pentadiene)s in terms of percent cis-1,2-, cis-1,4-, trans-1,4-, and 3,4-pentadiene units.     

Studies in the furan series

A study was made of certain transformations of the bicyclic compounds of the fur an series synthesized from 3,4-bis(chloromethyl)furan, N-butyl-4H, 6H-furo [3,4-c]pyrrole and 4H,6H-thieno[3,4-c]furan. On the basis of the same dichloride, 3,4-dimethyl furan and furan-3,4-dialdehyde were synthesized.For part XLVI, see [10].     

Effect of the homogeneity of the column set on the performance of a simulated moving bed unit. I. Theory

Although it is impossible to manufacture identical columns for use in a simulated moving bed (SMB) process, theoretical studies assume that all the columns in an SMB unit have identical characteristics. In practice, calculations in modeling and optimization studies are made with the average values of each column parameter set. In this report, the effects on SMB process performance caused by column-to-column fluctuations of the parameters are discussed. As a first step, we show how the differences in porosity of the columns may be taken into account with a revised set of separation conditions. Reductions in the purity of the extract and the raffinate streams are quantitatively related to the column-to-column fluctuations of the retention times of the two components arising from these porosity differences. For the sake of simplicity, the discussion first addresses the case of a four-column SMB operating under linear conditions. Then, the scope is extended to the cases of SMB units incorporating several columns in each section and to SMB units operating under nonlinear conditions.     

Separation and identification of organic and organometallic compounds by use of a liquid chromatography-particle beam-glow discharge mass spectrometry combination

Evaluation of the particle beam glow discharge mass spectrometry (PB-GDMS) system as a detector for liquid chromatography (LC) is described for the analysis of polycyclic aromatic hydrocarbons, steroids, selenoamino acids, and alkyllead compounds. A particle beam interface is used to introduce analyte species from the LC into a glow discharge source for subsequent vaporization and ionization. Mass spectra display classic EI fragmentation patterns for the organic compounds, as well as elemental and molecular information for the organometallic compounds. Chromatographic separations display good temporal correlation between UV and PB-GDMS detection modes. Detection limits for Pb in lead nitrate, triethyllead, and triphenyllead fall in the sub-ppb (ng) range.     

Electromagnetic interactions with rough metal surfaces

When surfaces are structured on the scale of the wavelength, we can expect incident light to be strongly modified by the surface. This is especially the case when the surface is metallic. We have developed a formalism for computing these modifications, closely analogous to electron scattering theory, which we briefly review and present some results for optical properties of, and electron energy loss in, colloids. Our main theme is another effect associate with rough or structured metallic surfaces: Surface Enhanced Raman Scattering, or SERS. We model the rough surface by a periodic array of spheres and obtain the correct magnitude for the enhancement and for the frequency shifts observed.     

Perturbation approach for frequency shifts in IR spectra of molecular clusters

A second order perturbation approach for the evaluation of the splitting and shifting of the infrared vibrational bands of molecular clusters, based on early publications of Buckingham, is presented. The Hamiltonian of the system comprises harmonic- and anharmonic intramolecular vibration terms, as well as the intermolecular potential. The anharmonic contributions of the intramolecular force field and the intermolecular potential are treated as a perturbation. In order to extend the applicability of the approach to homogeneous molecular clusters, the formalism of degenerate perturbation theory is employed. The new approach is applied to methanol clusters from dimer to hexamer for calculating the frequency shifts of the OH stretching mode (ω₁=3681.5 cm^?1), the CH₃ rocking mode (ω₇=1074.5 cm^?1), and the CO stretching mode (ω₈=1033.5 cm^?1). The numerical results compare favourably with experimental and previous theoretical data (except for ω₁), but with a tendency to overestimate the shifts.     

Oxidative addition of some geminal halonitroalkanes to iridium(I) and platinum(0) compounds

Oxidative addition of 1-chloro-1-nitroethane to trans-IrCl(CO)-[P(CH₃)₂C₆H₅]₂ followed by treatment of the initial product with pyridine yields a new iridium(III) complex IrCl(py)[COC(NO₂)CH₃][P(CH₃)₂C₆H₅]₂, whose structure has been confirmed by X-rays crystallography. Two intermediate products have been observed by NMR spectroscopy; their structures have been tentatively assigned. The reaction of the corresponding bromine derivatives yields two isomers of the composition IrBr₂(CO)[CH(NO₂)CH₃][P(CH₃)₂C₆H₅]₂, and these are not affected by pyridine. The reaction of 1-chloro-1-nitroethane with Pt[P(C₆H₅)₃]₄ takes a completely different course in that yields nitrorethane and cis-PtCl₂[P(C₆H₅)₃]₂ as the main products, with no detectable formation of the products of oxidation addition. A brief mechanistic investigation points towards the participation of radicals and radical anions as transient intermediates and a mechanism is proposed which explains most of the experimental results.     

Production of electronically excited NF by the reaction of fluorine atoms with HN3

Electronically excited NF in both the a¹Δ and b ¹Σ⁺ states hasbeen observed from the reaction of fluorine atoms with HN₃. The results suggest that fluorine atoms first abstract the hydrogen atom from HN₃, then react with the remaining N₃ to form NF^≠(a¹Δ). NF^*(b¹Σ⁺) is produced by a subsequent energy pooling reaction between NF^≠(a¹Δ) and vibrationally excited HF. The rate of the F + N₃ reaction is estimated to be ≈ 10¹² and ³ mole^?1 s^?1.