Determination of inelastic critical scattering at a first order phase transition in the CDW structure of 1TTaS2 using Mössbauer diffraction

We report Mössbauer diffraction measurements of the temperature dependence of the elastic and inelastic intensities at the (100) Bragg reflection in 1TTaS₂. These measurements use a newly developed microfoil conversion electron (MICE) spectrometry. They cover the temperature range from 19°C to 100°C, bracketing the first order 1T₁ to 1T₂ phase transition in the charge density wave structure at 79°C. The elastic Bragg peak shows a discontinuity at the phase transition as reported by Moret and Colella. The inelastic scattering shows a significant peak near the phase transition. This peak is interpreted as inelastic critical scattering at this first order phase transition.     

Studies on Antifungal Agents. Part 22. 3-aryl-5-[(aryloxy)alkyl]-3-[(1H-imidazol-1-yl)methyl]-2-methylisoxazolidines and related derivatives

The synthesis and antifungal activity of a novel series of 3-aryl-5-[(aryloxy)alkyl]-3-[(1H-imidazol-1-yl)-methyl]-2-methylisoxazolidines and related compounds, are discussed. The synthesis of the title compounds was accomplished via a 1,3-dipolar cycloaddition of α-substituted ketonitrones with l-alkenyl phenyl ethers (Scheme 2 and 3). The compounds were evaluated for in vitro antifungal activity in solid agar cultures against a broad variety of yeast and systemic mycoses and dermatophytes. While antifungal activity was evident throughout the series, in general, derivatives having halogen atom(s) in either or both aryl rings demonstrated the highest potency, especially against Trichophyton rubrum and Candida albicans. The dichloro analog 20 (PR 967-248) was found to possess the most useful activity. Its minimum inhibitory concentration (MIC) values ranged between 0.2 and 2.0 μg/ml, as compared to 0.2–20.0 μg/ml for the standard drug ketoconazole (4).     

Single-shot Thomson scattering on argon plasmas created by the Microwave Plasma Torch; evidence for a new plasma class

To determine the fine-structure size of plasmas created by a Microwave Plasma Torch (MPT), single-shot Thomson scattering (TS) measurements were performed. The aim was to find a solution for the long-standing discrepancy between experiments and Global Plasma Models (GPMs). Since these GPMs are based on the assumption that (ambipolar) diffusion is the main loss process for charged particles, the diffusion length and thus the fine-structure size should be known with high precision before an appropriate theory-experiment comparison can be carried out. In order to avoid the effect of blurring, which is created during the accumulation of multi-shot TS signals and which obscures the fine-structures, single-shot measurements are indispensable to determine the diffusion length.     

Low temperature NH(X 3sigma-) radical reactions with NO, saturated, and unsaturated hydrocarbons studied in a pulsed supersonic laval nozzle flow reactor between 53 and 188 K

The reactions of ground-state imidogen radicals (NH(X 3sigma-)) with NO and select saturated and unsaturated hydrocarbons have been measured in a pulsed supersonic expansion Laval nozzle flow reactor in the temperature range 53-188 K. The rate coefficients for the NH + NO system display negative temperature dependence in the temperature regime currently investigated and a global temperature-dependent fit is best represented in a modified power law functional form, with k1(NH + NO) = (4.11 +/- 0.31) x 10(-11) x (T/300)(-0.30+/-0.17) x exp(77+/-21/T) cm3/s. The reactions of NH with ethylene, acetylene, propene, and diacetylene were measured over the temperature range 53-135 K. In addition, the reactions of NH with methane and ethane were also measured at 53 K, for reasons discussed later. The temperature dependence of the reactions of NH with the unsaturated hydrocarbons are fit using power law expressions, k(T) = A(T/300)(-n), and are as follows: k4 = (2.3 +/- 1.2) x 10(-12) x (T/300)(-1.09+/-0.33) cm3/s, k5 = (4.5 +/- 0.3) x 10(-12) x (T/300)(-1.07+/-0.04) cm3/s, k6 = (5.6 +/- 1.9) x 10(-12) x (T/300)(-1.23+/-0.21) cm3/s, and k7 = (7.4 +/- 1.8) x 10(-12) x (T/300)(-1.23+/-0.15) cm3/s for ethylene, acetylene, propene, and diacetylene, respectively. The rate for NH + ethane at 53 K is measured to be k3 = (6.8 +/- 1.7) x 10(-12) cm3/s, while that for methane at the same temperature represents an upper bound of k2 < or = (1.1 +/- 4.3) x 10(-12) cm3/s, as this is at the limits of measurement with our current technique. The behavior of these systems throughout the temperature range explored indicates that these reactions occur over a potential energy surface without an appreciable barrier through a complex formation mechanism. Implications for chemistry in low temperature environments where these species are found are briefly discussed.     

The determination of the gamma isomer content of hexachlorcyclohexane dipwashes

The gamma BHC content of dipwashes has been deterimined satisfactorily by a cryoscopic method. The dipwash is treated with chromic acid to precipitate the total BHC and to destroy much of the organic impurity. Portions of the isolated impure BHC arc dissolved in both benzene and pure gamma BHC. By measurement of the resultant freezing point depression of the solvents, the proportion of gamma isomer in tho original sample can be calculated. The principle of the method should be applicable to other systems where the determination of one component in a multi-component mixture is required.     

Synthesis and structural characterization of hexa-tert-butyl-hexa-peri-hexabenzocoronene, its radical cation salt and its tricarbonylchromium complex

The hexa-tert-butyl substituted hexa-peri-hexabenzocoronene was synthesized in an overall yield of 83% from 4-tert-butylphenylacetylene. The key step was the oxidative cyclodehydrogenation of hexa(4-tert-butylphenyl)benzene with anhydrous FeCl3 in CH2Cl2 The high solubility of hexa-tert-butyl-hexa-peri-hexabenzocoronene in common organic solvents allowed a comprehensive spectroscopic characterization of this compound in solution. Electrochemical oxidation at -30 degrees C in the presence of tetrabutylammonium hexafluoroarsenate led to the formation of a stable radical cation salt. Reaction of hexa-tert-butyl-hexa-peri-hexabenzocoronene with an excess of tricarbonyl(naphthalene)chromium in THF/dioxane afforded a mixture of mono- and bis-tricarbonylchromium complexes which could be separated by chromatography. The molecular structures of the parent compound, its radical cation salt and its mono- tricarbonylchromium complex were determined by X-ray analysis and discussed in detail. Remarkably, the crystal structures of these compounds are mainly dominated by the formation of dimers of the aromatic cores.     

An active spectroscopical study on the plasma parameters of an ICP

Various techniques to measure the electron density and temperature of a 100 MHz inductively coupled plasma (ICP) are compared with each other. Apart from passive spectroscopy of measuring the shape of (e.g. H(beta)) and the area under emission lines we explored the field of active spectroscopy. Non-intrusive and specific are the methods of diode laser absorption (DLA) of an argon 4s-4p transition and Thomson scattering (TS). Intrusive and global is the power interruption (PI) technique: the response of line (argon and analytes) and continuum emission is followed during PI. Finally, a combination of two active techniques, namely TS during PI, is studied. By using the different techniques on the same plasma condition (frequency, power and flows) this intercomparison will reveal the validity region of the various techniques. In this way a strong basis will be created for understanding plasma phenomena.