Formation of spinel from metal organic compounds

A magnesium-aluminum product, which can be used to form spinel, is prepared by the simultaneous hydrolysis of magnesium acetylacetonate and aluminum isopropoxide. Infrared spectrum and X-ray diffraction analyses show that the product is a magnesium substituted γ-alumina-like amorphous material. Spinel is formed slowly at ≈700–1250°C at a heating rate of 1O°C min⁻¹. A marked increase in crystallite size occurs between 1100 and 1200°C. Spinel powders consist of aggregates of plate-like particles. The kinetics of crystallization of spinel have been studied by X-ray measurements. The initial stage at each temperature proceeds rapidly in a short time. The final stage can be described in terms of the contracting square equation 1 − (1 − f)^1/2 = kt, the activation energy being 164 kJ mol⁻¹.     

Photochemistry of thioxanthones—IV. Spectroscopic and flash photolysis study on novel n-propoxy and methyl,n-propoxy derivatives

The spectroscopic properties of seven oil soluble n-propoxy and methyl, n-propoxy substituted thioxanthone structures have been examined in various solvents and the data compared to their photopolymerization efficiencies, photochemical stabilities and flash photolysis behaviours in solution. Absorption maxima, extinction coefficients, fluorescence and phosphorescence spectra and quantum yields have been measured. Generally, all the compounds exhibit low fluorescence and high phosphorescence quantum yields but the ratio is solvent dependent. These observations are consistent with the high photoreactivity of the molecules operating in the lowest excited triplet state which is nπ* in character. Photopolymerization rates of n-butyl methacrylate with N-diethylmethylamine co-initiator correlate with the absorption maxima and extinction coefficients of the thioxanthones and also the degree of quenching of their fluorescence by the amine, indicating the importance of electron transfer. In the absence of a tertiary amine, transient formation on micro-second flash photolysis in 2-propanol is associated with the ketyl radical formed by the lowest excited triplet state abstracting a hydrogen atom from the solvent. In the presence of a tertiary amine, both ketyl radical and radical anion (at longer wavelengths) are observed, the latter being formed via abstraction of an electron from the amine. This is confirmed by a flash photolysis study using amines of various ionization potentials where a correlation is observed with radical anion absorbance. A pH study confirms the identity of the transient species. Activation of the thioxanthone molecule in the 3 and 4 positions with a methyl group enhances initiator activity whereas substitution in the t-position deactivates the molecule through intra-molecular hydrogen atom abstraction.     

The spectral and magnetic properties of some chloro and bromo transition metal complexes of picolinic acid and a study of their performance as colouring materials for poly(vinyl chloride)

Complexes of picolinic acid with the chlorides and bromides of manganese(II), iron(II), cobalt(II), nickel(II) and copper(II) have been prepared. Spectral and magnetic studies have shown that the iron complexes have discrete octahedral structures while the other complexes have polymeric octahedral structures. The decomposition of the complexes was studied by thermogravimetry and differential thermal analysis. The performance of the complexes as colouring materials for poly(vinyl chloride) has also been investigated.     

Electronic absorption spectra of 5- and 6- fluoroindoles

The electronic absorption spectra of 5-and 6-fluoroindoles, corresponding to the λ2850 Å system of indole, have been recorded in the vapour phase and analysed, assuming C_s symmetry for the molecules. The observed band system in both the molecules which lies in the region λ3100–2680 Å has been identified as a π* ← π transition corresponding to a ¹A′ ← ¹A′ transition. The i.r. spectra of these molecules have also been recorded and analysed and the results are used in the analyses of the electronic spectra. These show that there is not much change in the shape and very little change in size of either of these molecules in the excited electronic states.     

Comparison of a very high frequency 148 MHz inductively coupled plasma to a 27 MHz ICP

Physical parameters and analytical performance are determined for an analytical ICP operated at 148 MHz, a frequency nearly three times higher than any previously reported. The iron(I) excitation temperatures are approximately 1.5 times lower and the electron densities are five times lower than at 27 MHz. The consequences of these changes are lower analyte and background continuum emission intensities, such that the signal to background ratios are decreased at the higher frequency. Freedom from interferences and working curve linearity are unaffected while ease of sample introduction is improved. A shift towards atomic emission indicates a deviation farther from LTE at 148 MHz. These effects are attributed to the decrease in skin depth with increasing frequency.     

Raman and infrared studies of NaLa(MoO4)2:Nd3+

The polarized Raman and i.r. (powder) spectra of 0.5 mole % neodymium doped NaLa(MoO₄)₂ have been analysed on the basis of C_4h crystal symmetry. Group theoretically predicted fundamentals have been observed. The frequencies and intensities are not altered due to doping.