Parallel features

The low-spin manganese(n) complex [Mn(dppe)2-(CO)(CNBu)]2+ gave us a textbook example of a well-behaved ESR spectrum characterized by coincident g- and hyperfine-matrix principal axes. The nearly identical complex [Mn(dppm)2(CO)(CN)]+, (dppm = Ph2PCH2PPh2) (ref. 25) provides us with a good example of non-coincident principal axes. The frozen solution spectrum (Figure 4.8) shows that the parallel features are not evenly spaced. 

Figure 4.14 shows the ESR spectrum of [Mn(CO)(dmpe)Cp]+. Clearly, the parallel features are rather variable in line width, with the low-field lines broad and the high-field lines narrow. The ESR parameters for this spectrum49 are given in Table 4.15 where (j is the angle between the g-matrix z-axis and the hyperfine matrix z-axis. 

Because of the non-coincidence of the g- and -matrix principal axes, the various parallel features correspond to different orientations of the magnetic field in the g-matrix principal axis system. These orientations are given in Table 4.16. 

Table 4.16 Analysis of widths of parallel features of the spectrum of [Mn(CO)(dmpe)Cp]+.48 (Data from ref. 48 with permission, copyright (1997) American Chemical Society.)...

Oxidation of ortho-xylene. The spectra of the adsorbed species arising from interaction of ortho-xylene with the surface of the vanadia-titania catalyst in the presence of oxygen are shown in Figure 4. The spectra show some parallel features with respect to those discussed above concerning the oxidation of toluene and meta- and para-xylene. Also in this case the o-methyl-benzyl species begins to transform above 373 K, with production of adsorbed o-tolualdehyde (band at 1635 cm 0 and of a quinone derivative (band at 1670 cm. Successively bands likely due to o-toluate species (1530,1420 cm 0 grow first and decrease later with production of CO2 gas. 

The structure of this chapter (see Fig. 8.1) is based on the parallel features of the two types. We shall finally say something about the advantages of combining the two types, and make a few general observations on stability. 

A slightly different picture with many parallel features is shown in Figure 11.2. The figure shows three idealized dislocation loops, each loop being the edge of an incomplete lattice plane. Again we have a portion of the system subjected to compression [Pg.84]

To use the parallel features of a high performance computing facility, the software has to meet parallel demands, too. A numerical problem that has to be solved in parallel must be divided into subproblems that can be subsequently delegated to different processors. This partitioning procedure can be done either with so-called domain decomposition (Fig. 5) or functional decomposition (Fig. 6). 

The zero-field splitting Z) can be measured from the powder spectrum as schematically shown in Eig. 3.22 for a triplet state (S = 1). The maximum separation between the outermost peaks of 2D are parallel features with an absorption-like tine shape in the 1st derivative spectrum while the perpendicular tines separated... 

The three Ams = 1 transitions, (ms = 3/2 -o- lA, ms = lA -o—lA, ms = -Vi 3/2) give rise to perpendicular and parallel features for the S = 3/2 species with axial symmetry in Fig. 3.23. The parallel lines are separated by 2D, the perpendicular by D, as in the case of triplet state spectra, under the high-field approximation with the zero field splitting D hv (the microwave energy). 

F. 4.10 Schematic appetitance of the powder spectium of a triplet state. Axial symmetry is assumed so that the Ants = 1 perpendicular and parallel features are separated by D and 2- D, respectively. The = 1 -> -1 Ants = 2 transition is a single, narrow line, unaffected by anisotropy of the zfs... 

From the Formal Graph in the case study abstract, recognition of the parallel feature is obvious for the two paths starting from the current and converging toward the electric potential when one considers the concomitance of both capacitive and resistive processes. In the present case of strongly correlated parallel processes, attribution of an equal weight to each one and application of the paths complement tale, introduced previously in Section 10.1.3, are immediately translated into operator multiplication... 

Standard micrometers are good for measuring flat and parallel features and outside diameters. However, if the feature to be measured is curved, as in the wall thickness of a tube, an accurate measurement cannot be achieved. In this case a ball or roller can be placed on the inside wall of the tube and a measurement taken (Fig. 6.29). 

Figure 1. ESR spectra at 77 K of vanadium-doped (a) alumina- and (b) titania-pillared samples. Vertical lines are drawn to facilitate comparison of parallel features of the spectra.

The need for accurate computational procedures to evaluate detailed properties of gas phase chemical reactions is evident when one considers the wealth of information provided by laser, molecular beam and fast flow experiments. By stressing ordinary scalar computers to their limiting performance quantum chemistry codes can already provide sufflciently accurate estimates of the stability of several small molecules and of the reactivity of a few elementary processes. However, the accurate characterization of a reactive process, even for small systems, is so demanding in terms of computer resources to make the use of supercomputers having vector and parallel features unavoidable. 

In all these cases, to have a good statistics (i.e. to have a significant sample of reactive events) one has to run a large number of trajectories. Therefore to obtain results in a reasonable time the cpu consumption per single trajectory has to be very short. This is possible only when using supercomputers provided that the programs have been restructured to take advantage of the vector and parallel features of these machines. 

A careful restructuring of a quasiclassical trajectory code and the adoption of a polynomial representation of the potential energy has made it possible to take profit from both vector and parallel features of the IBM 3090/200 VF supercomputer to perform extended calculations of the reactivity of some alkali/alkaline earth -f- hydrogen halide systems. Thanks to the reduction of the needed cpu time it has thus been possible to examine in detail the dynamics of these reactions. In particular, it has been possible to improve ab initio potential... 

For the out-of-plane variations of phi, Emtp again displayed parallel features to Ec- Thus for both Cl and Br, one maximum for found at 180°, and two minimum-energy regions at 60-120° and 240-300°. For F, the curve was virtually flat throughout. 

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