Rhombic component

Ammonium sulfate [7783-20-2], (NH 2 U4, is a white, soluble, crystalline salt having a formula wt of 132.14. The crystals have a rhombic stmcture d is 1.769. An important factor in the crystallization of ammonium sulfate is the sensitivity of its crystal habit and size to the presence of other components in the crystallizing solution. If heated in a closed system ammonium sulfate melts at 513 2° C (14) if heated in an open system, the salt begins to decompose at 100°C, giving ammonia and ammonium bisulfate [7803-63-6], NH HSO, which melts at 146.9°C. Above 300°C, decomposition becomes more extensive giving sulfur dioxide, sulfur trioxide, water, and nitrogen, in addition to ammonia. 

Insoluble Sulfur. In natural mbber compounds, insoluble sulfur is used for adhesion to brass-coated wire, a necessary component in steel-belted radial tires. The adhesion of mbber to the brass-plated steel cord during vulcanization improves with high sulfur levels ( 3.5%). Ordinary rhombic sulfur blooms at this dose level. Crystals of sulfur on the surface to be bonded destroy building tack and lead to premature failure of the tire. Rubber mixtures containing insoluble sulfur must be kept cool (<100°C) or the amorphous polymeric form converts to rhombic crystals. 

The axial resonance is assigned to ruthenium A with its D4h local symmetry (compare gj = 2.51, gy = 1.64 in traw.s-RuCl4(PEt3)J) while the rhombic signal is assigned to ruthenium B , where the local symmetry is D2h and three different components of the g-tensor are expected. 

In Fig. 8.8, we see that sulfur can exist in any of four phases two solid phases (rhombic and monoclinic sulfur), one liquid phase, and one vapor phase. There are three triple points in the diagram, where various combinations of these phases, such as monoclinic solid, liquid, and vapor or monoclinic solid, rhombic solid, and liquid, coexist. However, four phases in mutual equilibrium (such as the vapor, liquid, and rhombic and monoclinic solid forms of sulfur, all in mutual equilibrium) in a one-component system has never been observed, and thermodynamics can be used to prove that such a quadruple point cannot exist. 

If D is taken as a traceless tensor, Tr(/)) = Da = 0, there remain only two independent components for D (neglecting the three Euler angles for orientation in a general coordinate system). Usually, these are the parameters D and E, for the axial and rhombic contribution to the ZFS ... 

The values of the rhombicity parameters are conventionally limited to the range 0 < EjD < 1/3 without loss of generality. This corresponds to the choice of a proper coordinate system, for which /)zz (in absolute values) is the largest component of the D tensor, and /) is smaller than Dyy. Any value of rhombicity outside the proper interval, obtained from a simulation for instance, can be projected back to 0 < EID < 1/3 by appropriate 90°-rotations of the reference frame, that is, by permutations of the diagonal elements of D. To this end, the set of nonconventional parameters D and EID has to be converted to the components of a traceless 3x3 tensor D using the relationships... 

The hyperfine coupling tensors of carotenoids were determined from the HYSCORE analysis of the contour line-shapes of the cross-peaks (Dikanov and Bowman 1995,1998, Dikanov et al. 2000), which provided the principal components of the tensors that appear to be rhombic. Such tensors are characteristic of planar conjugated radicals with the unpaired spin in a pz orbital of the carbon of the C-H group. 

In order to illustrate the general applicability of the methodology we have extended our approach to other large zeolite crystals, such as SAPO-34, SAPO-5 and ZSM-5. Our study on the rhombic SAPO-34 crystals reveals a four-pointed star fluorescence pattern at 445 K, which is transformed into a square-shaped feature at 550 K. This is illustrated in Figure 4a. Confocal fluorescence slices, summarized in Figures 4b-d, recorded at different temperatures show the cubical pattern, which proceed from the exterior of the crystal inwards. Both observations are consistent with a model which involves six components of equal tetragonal pyramids as illustrated in Figure 3b. 

Working first with Polanyi, Weissenberg, and Brill, and later as the leader of the Textile Chemistry Section, Mark successively published papers on the crystal structures of hexamethylenetetramine, pentaerythritol, zinc salts, tin, urea, tin salts, triphenylmethane, bismuth, graphite, sulfur, oxalic acid, acetaldehyde, ammonia, ethane, diborane, carbon dioxide, and some aluminum silicates. Each paper showed his and the laboratory s increasing sophistication in the technique of X-ray diffraction. Their work over the period broadened to include contributions to the theories of atomic and molecular structure and X-ray scattering theory. A number of his papers were particularly notable including his work with Polanyi on the structure of white tin ( 3, 4 ), E. Wigner on the structure of rhombic sulfur (5), and E. Pohland on the low temperature crystal structure of ammonia and carbon dioxide (6, 7). The Mark-Szilard effect, a classical component of X-ray physics, was a result of his collaboration with Leo Szilard (8). And his work with E. A. Hauser (9, 10, 11) on rubber and J. R. 

In addition, it is worth mentioning that, even in the case of a uniform distribution, the number of vectors oriented parallel to any given direction is small, so that pmax could be underestimated. Here we assumed that the rotational diffusion tensor is axially symmetric. The presence of a rhombic component could be identified by the shape of the distribution of the values of p (see e.g. Refs. [55, 57]). 

The next stage is to choose a reference compound of the type 1 component. Unless it is very far from stable in the system, it is advantageous to choose the element, rhombic sulphur in this case. 

The static ZFS, which is present in low-symmetry complexes, affects mainly the energy level fine structure. It is described by axial and rhombic components, D and E. Its effects on nuclear relaxation depend on two angles, 9 and cj), defining the position of the nucleus with respect to the ZFS principal tensor axes. Figure 23 shows the dispersion profiles for different values of S, D, E and 9. Many such examples are reported in Chapter 2. 

However, ab initio calculations [QCISD-(T)/6-31G //UMP2/6-31G ] on ethylene and its radical cation support an anti -7i-complex, in which the two components are joined by one long bond (190 pm), rather than the sandwich -type 71 complex. The complex is connected to two transition states leading to a (rhombic) cyclobutane radical cation (see above) or, by 1,3-H-shift, to 1-butene radical... 

From the anisotropic contributions to the HFCs, it is confirmed that the reduced site is the main source of anisotropy in the system. The computed values reproduce the rhombicity of all anisotropic hyperfine tensors, but there is a clear tendency of overestimation. In any case, since the anisotropic components are at least an order of magnitude smaller than the isotropic contributions to the HFC, it is more appropriate and useful to focus on the latter. All isotropic HFCs have the correct signs with respect to the... 

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