F. Gubitz

A simple explanation of unexpected efg's in19F-TDPAD measurements

In our19F — TDPAD experiments often efgs are appearing, which are due to bonds of the probe nucleus that do not exist in the target substance. A simple mechanism is proposed to explain these unexpected coupling constants in molecular crystals.

QUADRUPOLE INTERACTION OF 111CD IN THE SEMICONDUCTOR CDS

The time differential perturbed angular correlation technique was applied to study the electric quadrupole coupling of 111Cd in the II‐VI semiconductor CdS (20 K≤T≤1000 K). Two kinds of sample preparation were used: implantation and diffusion. Obtained results for the regular lattice sites were independent of the preparation. The measured electric field gradient (EFG) was between 6.7±0.4 MHz and 9.1±0.2 MHz. Data were confirmed by point‐charge calculations. Implantation however caused a second EFG (≊78 MHz) that was assigned to a defect due to the preceding irradiation.

Nuclear quadrupole interaction in solid HF and trifluoroaminoboranes

Abstract Using the time differential perturbed angular distribution method (TDPAD) solid HF and trifluoroaminoboranes have been investigated. In the case of solid HF some new aspects appear in the interpretation of former experiments. The new measurements either reproduce the older data that yielded one frequency and a distinct ν, or show two frequencies and no distinct ν. This discrepancy can be explained with different target preparations. While the one-frequency experiments were done with untempered targets the two-frequency targets were tempered. Trifluoroaminoboranes (F 3 BNH 3 ) are known as charge-transfer complexes. Since ammonia acts preferentially as an electron donor and 19 F is the most electronegative element, a lowering of the observed coupling constant should appear. Experiment, however, does not support this; it gives an unchanged coupling constant, but the asymmetry parameter is changed by a factor of more than 2. This behaviour can be understood by calculating the electron distribution in both molecules within the framework of the Townes and Dailey theory. It turns out that charge transfer does take place, but the transferred charge does not lead to a more isotopicc electronic environment for fluorine, but rather reduces the asymmetric population of its p x and p ŷ orbitals.

Electric quadrupole interaction of111Cd in the system Sb1−xMx (M=Ag,Cd,In,Sn), Sb2Te3, Bi2Te3 and In2Te3

We have performed TDPAC-measurements to investigate the static quadrupole interaction of111Cd in the classic semimetal Sb. The coupling constant depends on the concentration of small amounts of metal admixtures. The only exception is the system Sb1−xAgx. The temperature dependence of the efg in the narrow gap semiconductors Sb2Te3 and Bi2Te3 is similar to that one in Te. In contrast to these results the efg in the III–VI-semiconductor In2Te3 is temperature independent.

The electric hyperfine interaction in some covalent bonded fluorine molecules

Abstract With the time differential perturbed angular distribution method (TDPAD) we have investigated the electric hyperfine interaction in the fluorine molecule, group IV tetrafluorides and group V trifluorides. The value of the efg for the F 2 -molecule is in good agreement with recent theoretical calculations. The results for the tetra- and trifluorides are discussed in the framework of the Townes and Dailey theory.

The electric hyperfine interaction in the F2-Molecule and in some tri- and tetrafluorides

The quadrupole coupling constants in the fluorine molecule and in the group V trifluorides and the group IV tetrafluorides have been measured. In the case of fluorine the value of the resulting efg is in good agreement with recent theoretical calculations; the other results are discussed in the framework of the Townes and Dai1ey theory.

The electric hyperfine interaction in group VI-a hexafluorides

The electric hyperfine interaction in group VI-a hexafluorides SF6, SeF6 and TeF6 has been studied in the temperature range from 10 K to about 110K by means of the TDPAD method. The temperature dependence can be explained by Bayer — Kushida theory. The coupling constants decrease with increasing temperature. The strength of the temperature dependence diminishes from SF6 to TeF6, indicating an increase of ionicity of the bonds. If the coupling constants are plotted versus the elements of the fluorine compounds, characteristic trends can be seen. Therefore we predict the coupling constant of OF2 to be about 100 MHz

Electric field gradients in interhalogenic compounds

The time differential perturbed angular distribution me thod has been applied to investigate the electric field gradient in the interhalogenic compunds C1F, BrF3 and 1F5 Measurements at different temperatures revealed an unexpected behaviour of the modulation amplitude. Since for this behaviour no consistent explanation can be given yet, data are reported only.

Some results of TDPAD measurements in fluorine compounds

Abstract In recent years a great variety of compounds containing 19 F have been investigated. By plotting the data in a suitable manner general trends in the behaviour of the coupling constants can be recognized. These trends enable us to predict the coupling constants of as yet unexamined simple fluorine containing compounds. One of these is OF 2 for which, according to the behaviour of the compounds on which our predictions are based, a 19 F coupling constant of approximately 100 MHz is expected. In analogy to the work done on trifluoroaminoboranes the electron distribution of the CF bond in different organic molecules is determined. Also some data gained from experiments performed with fluorinated aromatic compounds are given.

The electric hyperfine interaction for 111Cd in the systems Sb1−xMx (MAg, Cd, In, Sn), Sb2Te3, Bi2Te3 and In2Te3

Abstract Using the TDPAC-method the electric quadrupole interaction and its temperature and concentration dependence has been measured for different systems. In the semimetal Sb the temperature dependence of the coupling constant depends on the concentration of small amounts of metal admixtures. In the narrow gap semiconductors Sb 2 Te 3 and Bi 2 Te 3 the efg increases with temperature. In contrast to these results the efg in the III–VI-semiconductor In 2 Te 3 is temperature independent.