Kinetics and mechanism in the decomposition of NH3 in a radio-frequency pulse discharge

Studies of time-resolved absorption spectra of transient species in the decomposition of NH₃ by an r.f. pulse discharge together with product analysis showed that the major radical formed was NH at concentrations of the order of 10^–6 mol dm^–3 (10⁵ molec. cm^–3). Possible mechanisms for the formation of the radical during the discharge and its decay following pulse cut-off were tested by computer simulation of the kinetic data. Following zero-order formation with rate coefficient 0.19±0.03 mol dm^–3 s^–1, the decay was second order in NH with rate coefficient 2.1±0.5×10⁹ mol^–1 dm³ s^–1 both for pure NH₃ and where NH₃/rare gas mixtures were investigated. The kinetic data are consistent with NH removal in a nonassociative radical-radical reaction proceeding via a short-lived collision complex, probably 2NH N₂H₂ N₂ + H₂.     

The dynamic performance of the Weissenberg Rheogoniometer

The dynamic performance of a standard Model R18 Weissenberg Rheogoniometer has been studied in detail. The Rheogoniometer was carefully calibrated and used to measure accurately the rheological behaviour of a highly nonlinear viscoelastic polymer solution (1% polyacrylamide in 50% glycerol/water).In this paper the elaborate procedures that were used to calibrate the electronic signal processing equipment are described. The various static and dynamic calibration/correction factors are defined and incorporated into a computer implemented calculation scheme for evaluating the linear dynamic properties from the raw digital transfer function analyser readings.The linear dynamic properties of the polymer solution are presented together with the corresponding steady shearing properties. Both cone and plate and parallel plates geometries were used and good agreement was obtained over the wide range (six decades) of frequencies and shear rates employed.Fluid inertia effects were found to become important when the modified Reynolds number,Re _c ² orRe(H/R)², exceeded a value of about 0.1. These effects had a strong influence on the phase angle() which could readily be detected by varying the gap angle/width. The Walters-Kemp equations were found to give consistently accurate values for the linear dynamic properties for modified Reynolds numbers up to 11.6 which was the highest reached.     

Analyse der Alkohole

Analytical and Bioanalytical Chemistry -     

Crystallographically-based analysis of the NMR spectra of maghemite

All possible iron environments with respect to nearest neighbour vacancies in vacancy-ordered and vacancy-disordered maghemite have been evaluated and used as the foundation for a crystallographically-based analysis of the published NMR spectra of maghemite. The spectral components have been assigned to particular configurations and excellent agreement obtained in comparing predicted spectra with published spectra taken in applied magnetic fields. The broadness of the published NMR lines has been explained by calculations of the magnetic dipole fields at the various iron sites and consideration of the supertransferred hyperfine fields.     

Gerbstoff

Ohne Zusammenfassung     

Electrolyte conductivity of salts in hexamethylphosphotriamide

Precise conductivity measurements are reported for twenty-two 1:1 salts in hexamethylphosphotriamide at 25°C. The results have been analyzed using the full versions of the equations of Fuoss-Hsia and of Pitts for the conductivity of the free ions. TheK _A andΛ ^∞ values are consistent with strong cation solvation but weak anion solvation by the solvent. Earlier results for salts in related solvents have been reanalyzed for comparative purposes.