Diffusive motion of iron microcrystals studied by Mössbauer spectroscopy

A new model is presented which explains well the dramatic decrease of the Mössbauer line intensities with raising temperatures for freely dispersed iron microscrystals. In contrast to other theories which consider mainly vibration to be responsible we discuss here the decrease in terms of large amplitude diffusive rotational or translational jumps of the particles. Such diffusive jumps lead — in agreement with the observation — to a strong reduction of the Mössbauer-intensity without broadening the line width in a noticeable way. The typical potential well for a diffusing particle in an equilibrium position is derived quantitatively to be 13 meV. The model might be important also for a new understanding of the dynamics of catalytic clusters either in contact with each other or with larger solid surfaces.Part of this work was supported by the DFG Sonderforschungsbereich 306, Konstanz     

Trovacenchemie. 13 [1] Weg und Irrweg zu Di([5]trovacenyl)keton

Trovacene Chemistry. 13 [1] On Being Lead and Mislead in the Synthesis of Di([5]trovacenyl)ketone Di([5]trovacenyl)ketone ( 3¨ ) has been prepared from lithio‐[5]trovacene and dimethylcarbamoyl chloride and studied by X‐ray diffraction, cyclic voltammetry, magnetic susceptometry and EPR spectroscopy. Slight variation of the synthetic protocol affords an unusual trinuclear complex 5 ? that is also fully characterized. Spin‐spin exchange interaction is smaller in 3¨ than in 1,1‐di([5]trovacenylethene ( 2¨ ), which differs from 3¨ by a replacement of O for CH₂. The novel trinuclear complex 5 ? , however, displays exchange coupling very similar to that observed in 1‐methoxy‐2,5,6‐tri([5]trovacenyl)benzene ( 7 ? ). In both cases, an unsymmetrical triangular arrangement of S = 1/2 centers is encountered. These findings are discussed in terms of the nature of the respective spacers.     

Temperature dependence of hyperfine fields in intermediate valent140CeLa and140CeLu

The hyperfine fields for the systems¹⁴⁰CeLa and¹⁴⁰CeLu have been determined by time differential perturbed angular correlations (TDPAC) in the temperature range 4.2 K≤T≤330 K. Magnitude and temperature dependence of the paramagnetic enhancement factor β indicate that cerium in either system is of intermediate valence. This behaviour is discussed in terms of a theory proposed by Ramakrishnan et al. [1–3].     

Precision of a dual energy X-ray absorptiometry device

The standard method to diagnose and follow-up osteoporosis is the measurement of bone mineral density (BMD) using dual X-ray absorptiometry (DEXA). Manufacturers' manuals of DEXA devices state the intrascanner coefficient of variance is less than 0.01 g/cm². The aim of this study was to evaluate the in vivo coefficient of variance of a Lunar DPX scanner in male and female healthy adult subjects. Average BMD for females and males were 1.170±0.091 g/cm² and 1.272±0.115 g/cm², respectively. Monthly phantom measurements provided and controlled by the manufacturer were 1.243±0.008 g/cm² (range 1.222 to 1.257) and the coefficient of variance was 0.006. It is concluded that the in vivo coefficient of variance of DEXA devices can slightly be higher than that proposed by the manufacturer. This revised version was published online in August 2006 with corrections to the Cover Date.