Crystalline splitting

For polypropylene (PP), on the other hand, it has not been possible to observe any IR splittings resulting from intermolecular or crystalline packing. In fact, there are many features in the PP spectrum that look like pairs of bands, and indeed they are. However, the band pairs arise from intramolecular helical splitting, not from intermolecular crystalline splitting. Actually, intermolecular packing influences the IR spectrum of PP very little. In Fig. 4.42, the X-ray patterns of the monoclinic a phase and the smectic S phase are shown. The monoclinic a phase consists of well-ordered crystalline 31 helices, while the smectic S phase consists of 31 helices that are out of register with each other. The smectic phase will convert with time to the... 

Amphiphiles often have a complex phase behaviour with several liquid crystalline phases These liquid crystalline phases are often characterised by long-range order in one directior together with the formation of a layer structure. The molecules may nevertheless be able tc move laterally within the layer and perpendicular to the surface of the layer. Structura information can be obtained using spectroscopic techniques including X-ray and neutror diffraction and NMR. The quadrupolar splitting in the deuterium NMR spectrum can be... 

A calculation of tunneling splitting in formic acid dimer has been undertaken by Makri and Miller [1989] for a model two-dimensional polynomial potential with antisymmetric coupling. The semiclassical approximation exploiting a version of the sudden approximation has given A = 0.9cm" while the numerically exact result is 1.8cm" Since this comparison was the main goal pursued by this model calculation, the asymmetry caused by the crystalline environment has not been taken into account. 

In this article we have reviewed the results of a joint spectroscopic and morphological investigation of -sexilhienyl (T(J. The lowest singlet electronic level, which is assigned to I B , splits in the single crystal into four crystalline levels. The structure of the exciton band is investigated by the combined absorption and... 

Thus, two factors may be pointed out that determine the possibility of obtaining high yields of crystalline polyethylene on a solid catalyst with no diffusional restriction (1) the splitting up of the catalyst into small particles (< 1000 A), possible when using supports with low resistance to breaking (2) the formation of polymer grains with polydispersed porosity. 

Differences in the. solid-state NMR signals of crystalline forms having identical conformations have been also observed. For instance, well-crystallized a form samples of i-PP show splittings for the methyl (22.6, 22.1 ppm) and methylene resonances (45.2, 44.2 ppm) into two lines with relative intensities 2 1 [117,118]. These splittings have been interpreted in terms of the known crystalline packing of the a form, which is characterized by pairs of 3/1 helices of opposite handedness at closer distances (Fig. 10). This generates inequivalence between the carbons indicated as A and those indicated as B in Fig. 10 [117,118]. 

Fig. 13 Isotopic line splitting of the V3 stretching vibration in single crystalline (see also Fig. 12(a)), after [108, 109], The origin of each absorption band is indicated by an isotopomer present in crystals of natural composition. While the absorption could be fitted by a Lorentzian band profile, the remaining peaks were dominated by the Gaussian contribution in the Voigt band shapes (solid lines below the spectrum). The sum result of fitting the isotopic absorption bands is inserted in the measured spectrum as a solid line...

The resonance splitting of intramolecular modes in the crystalline state is often called Davydov splitting or factor group splitting . In contrast to the static field effects of the crystal, this splitting is due to the dynamical interaction of the constituents in the primitive cell... 

The last state in Fig. 11.1 that has not yet been discussed is the state of the neat liquid compound X. For liquid compounds this is the relevant initial state for solubility, but almost aU drug-Uke compounds are solid at room temperature. In this case the neat liquid is a virtual state of a supercooled liquid which can hardly be accessed experimentally. However, it is an interesting intermediate state because it allows us to split the calculation of solubility into two separate steps, which are conceptually and for some methods computationally easier to handle than the complete step from the crystaUine state of the drug to the liquid state of the drug dissolved in water. In the first step we only have to transfer the compound from its neat crystalline state to its neat liquid state. The free energy of this fusion transfer is usually called AG s (or if considered in the opposite direction). 

Distinct quadrupole shifts do occur as well in magnetically split spectra of single-crystals, poly crystalline powder or frozen solution samples. In all three cases, the line shifts obey the simple first-order expression at high-field condition. 

With h 6) - 1/sin 0)5(0 — Oq), one obtains the same result as given by (4.58), which implies that the anisotropy of the/factor cannot be derived from the intensity ratio of the two hyperfine components in the case of a single crystal. It can, however, be evaluated from the absolute/value of each hyperfine component. However, for a poly-crystalline absorber (0(0) = 1), (4.66) leads to an asymmetry in the quadrupole split Mossbauer spectrum. The ratio of l-Jh, as a function of the difference of the mean square amplitudes of the atomic vibration parallel and perpendicular to the y-ray propagation, is given in Fig. 4.19. 

The anisotropic/factor may also manifest itself in the relative line intensities of Zeeman split hyperfine spectra in a poly crystalline absorber. Expanding f(0) in a power series... 

A remarkable number of Mossbauer studies have been published since the first spectra reported in 1966 [135], most of them performed on the p-form when not specified differently [131, 132, 136-139]. Also, high pressure has been applied [140] and thin Aims were prepared [141]. Because of the ambiguity concerning the crystalline phase, the values of the hyperfine parameters show some dispersion. The isomer shift, 5 = 0.4-0.6 mm s is found in between the t3q>ical values known for high-spin iron(II) and low-spin iron(II). The quadrupole splitting is large, A q = 2.4-3.0 mm s (Table 8.3), as one might expect because of the unusual non-cubic symmetry. Applied-field measurements revealed positive F . 

Flint is a hard and easily split variety of the mineral quartz (composed of silicon dioxide), which occurs not only as flint but also in a wide range of other varieties. Some of these exhibit different colors and colored patterns and have characteristic crystalline structures, while others are amorphous (see Textbox 21). In all its varieties, nevertheless, the hardness of quartz is very high, being graded as 7 on the Mohs scale (see Textbox 23). Almost all varieties are either transparent or translucent and display a distinctive luster. These properties made quartz an attractive material for making ornamental... 

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