Powder doublet

The most remarkable pentammine is the hydride [Rh(NH3)5H]2+ [91], produced by zinc (powder) reduction of the chloropentammine salt. It shows u(Rh-H) at 2079 cm-1 in the IR spectrum (of the sulphate) and the low-frequency hydride NMR resonance at S = -17.1 ppm as a doublet showing Rh-H coupling (14.5 Hz). Its crystal structure shows the pronounced rraus-influence of hydride, with the Rh-N bond tram to H some 0.17 A longer than the cis Rh-N bond (Figure 2.45) [92]. 

In a conventional Fe Mossbauer experiment with a powder sample, one would observe a so-called quadrupole doublet with two resonance lines of equal intensities. The separation of the lines, as given by (4.36), represents the quadrupole splitting The parameter Afg is of immense importance for chemical applications of the Mossbauer effect. It provides information about bond properties and local symmetry of the iron site. Since the quadrupole interaction does not alter the mean energy of the nuclear ground and excited states, the isomer shift S can also be derived from the spectrum it is given by the shift of the center of the quadrupole spectrum from zero velocity. 

NFS spectra recorded at 300 K for -cut and c-cut crystals are shown in Fig. 9.17 [48]. The/factors for the two orientations were derived from the speed-up of the nuclear decay (i.e., from the slope of the time-dependent intensity in Fig. 9.17a and from the slope of the envelope in Fig. 9.17b). The factors obtained f ( P = 0.122 (10) and f = 0.206(10) exhibit significant anisotropic vibrational behavior of iron in GNP. This anisotropy in f is the reason for the observed asymmetry in the line intensity of the quadrupole doublet (in a conventional Mossbauer spectrum in the energy domain) of a powder sample of GNP caused by the Goldanskii-Karyagin effect [49]. 

The corresponding DSC curves of Mg powders milled in hydrogen atmosphere after various milling times under the HES mode are shown in Fig. 2.40. The 5 h milled sample has only one small peak at 410.5°C, but the others show double peaks (peak doublets). Desorption peak temperatures of the doublet peak first decrease as... 

Fig. 2.41 Representative DSC curves of MgHj powders synthesized by reactive milling for more than 20 h showing (a) peak with a shoulder (hidden peak) and a well-developed peak or (b) double peaks (doublet) (heating rate 4°C/min) [63]...

Fig. 2.42 DSC desorption temperature from Table 2.17 versus powder particle size (BCD) of synthesized MgHj powders, (a) Onset temperature (T ) and (b) low-temperature (LT) and high-temperature (HT) peaks in a doublet. Numbers beside data points indicate the grain size of the MgH phases [63]...

Thermal behavior of the milled (MgH + Zwt%NaAlH ) composites with X = 0,10, 30, 50 and 70 was investigated by DSC and TGA. DSC traces of MgH powder after milling for 5 h (not shown here) showed an endothermic peak doublet at 373.5 and... 

It is seen that both the powder and the crystal show four distinct peaks, marked 1, 2, 3 and 4 in Fig. 11. The remaining peak(s)are the spinning side bands, as verified by the fact that their relative positions change in proportion to the spinning frequency. The doublet around 250 ppm can be assigned to... 

An important observation was that the position of the coalesced peak (doublet) did not coincide with the average of the four low-temperature peaks this point is discussed in detail in the following section. The doubUng was not related to any crystal effects, because measurements with powders exhibited a similar sphtting [26]. 

Fig. 4. Quadrupolar powder patterns (a) Spin NMR powder pattern showing that the central -)<- ) transition is broadened only by dipolar coupling, chemical shift anisotropy, and the second-order quadrupolar interactions, (b) Spin 1 NMR powder pattern for a nucleus in an axially symmetric electric field gradient (see text). The central doublet corresponds to 6 = 90° in Eq. (10). The other features of low intensity correspond to 6 = 0° and 6 = 180°. (c) Theoretical line shape of the ) - -) transition of a quadrupolar nuclear spin in a powder with fast magic-angle spinning for different values of the asymmetry parameter t (IS) ...

THE RUBBER DIAPHRAGM INTENDED TO KEEP SOIL FROM SHRINKING AWAY FROM THE BOTTOM CELLOPHANE IS HERE USED TO PRESS THE DOUBLET TO A THIN GAP LIMITED BY POWDER... 

By inserting a hypodermic needle through the O-ring seal, this equipment was adapted to reverse osmosis experiments by using a cellophane doublet separated by a powder gap in place of the single cellophane used by Richards [14). After some difficulty with the reliability of the pressure system, fresh water was produced at the rate of 0.06 gallon per square foot per day. 

Distinct and different peak profiles of X-ray powder diffraction on [Fe(4,7-(CH3)2-phen)2(NCS)2] have been observed for the 5T2 and A, phases, respectively183). The intensities of the lines show the same temperature dependence and the same hysteresis behaviour as the area fractions of the HS and the LS quadrupole doublets, respectively, of the Mossbauer spectra. These studies183) provide clear evidence for a simultaneous change of the electronic spin state and of the crystallographic properties. 

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