Fine-structure parameters

Table 8 Fine Structure Parameters and Axial Elastic Moduli of PET Fibers of Microfibrillar Substructure...

Table 11 Thermal Volume Expansivity (a2s) and Related Fine Structure Parameters of Differently Drawn PET Fibers...

Comparing the alteration in a values with the established changes in fine structure parameters presented in Table 12, it can be seen that the alteration in a values does not correlate with variations in any particular structure parameter. This leads to the conclusion that the ascertained alternation in a must be evoked by a complex change in different substructure, microstructure, and orientation parameters of the fiber. 

The obtained Cp values and the established fine structure parameters for the PET fibers examined are presented in Fig. 8 and Table 13. 

Table 12 Fine Structure Parameters of Annealed PET Fibers...

The low electrical conductivity of PET fibers depends essentially on their chemical constituency, but also to the same extent on the fiber s fine structure. In one study [58], an attempt was made to elucidate the influence of some basic fine structure parameters on the electrical resistivity of PET fibers. The influence of crystallinity (jc) the average lateral crystallite size (A), the mean long period (L), and the overall orientation function (fo) have been considered. The results obtained are presented in the form of plots in Figs. 9-12. 

The difference between the fine structure parameters computed from the experimental g-tensor and those measured from the spectrum are presumed to be the electron dipolar contributions. 

The onset of sudden variations in vibrational fine structure is one of the most sensitive indicators of a change in resonance structure. The magnitudes of fine-structure parameters are determined by second-order perturbation theory (a Van Vleck or contact transformation) [17]. The energy denominators in these second-order sums over states are approximately independent of vib as long as the <01 <02 - 3/v-6 resonance structure is conserved. 

Since the perturbations turn on at slightly lower Vj than the onset of changes in fine-structure parameters [5], it seems likely that the perturbations in (0, 32, 0) are due mostly to new oohx 4oobend anharmonic resonances and the rapid changes in fine-structure parameters at (0, 36,0) due mostly to new oohx = 3oobend Coriolis resonances. 

In a smaller molecule (HCP), these diagnostically important changes in vibrational resonance structure are manifest in several ways (i) the onset of rapid changes in molecular constants, especially B values and second-order vibrational fine-structure parameters associated with a doubly degenerate bending mode (ii) the abrupt onset of anharmonic and Coriolis spectroscopic perturbations and (iii) the breakup of a persistent polyad structure 15]. 

For a linear molecule, only the 2 component of JTso is involved in the evaluation of diagonal matrix elements. In a Hund s case (a) basis,161 the fine-structure parameter Ae at the equilibrium geometry Qe can be obtained from... 

Calculations of the fine-structure parameters by Veseth,258 the spin-orbit contribution to the zero-field splitting,259 and the Verdet constant for O2 have also been reported.260... 

However, for n,ir triplet aromatic ketones and aldehydes, the increased spin delocalization onto the rings should reduce the zero-field splitting, and the failure of their ESR detection may be attributed mainly to their short lifetimes. Hayashi and coworkers (290) have examined the ESR fine-structure parameters of a number of molecular complexes in their phosphorescent state and have derived the dependence of the fine-structure values upon the degree of charge-transfer character in the lowest triplet state of the molecular complexes. Some of their results are collected in Table 15. 

Mossbauer spectroscopy can also be used to obtain information about fine structure parameters like zero-field splitting D and rhombicity parameter E D. The zero-field splitting is a second-order effect, which can be classically visualized as resulting from the circular currents generated in the atomic shell by the electron spin. In Section 3.10.5, we describe how D and E D can be calculated. 

The so-called fine structure parameters D and E were introduced to describe the zero-field splittings due to spin-spin interactions in organic molecules (e. g. see [32,90,130]). For transition metal compoimds and in the context of this review, these parameters simply give the energy separations (zfs) between the three triplet substates. 

From Sections 2 and 3 it will be clear that the shape of an EPR spectrum contains information on structure (g tensor, hyperfine splittings) and on interactions (fine structure parameters, exchange coupling). This has been exploited with much success in the study of the primary reactants in photosynthesis. In this section this will be highlighted for oxidized and reduced primary reactants in the bacterial reaction... 

Fine structure parameters Minimum, DZ Good representation of inner shells... 

Owing to the low values of their fine structure parameters and to their characteristic hyperfine pattern the thermally activated triplet states I, II, III,. .. are identified as diradical DR oligomers with the following symmetric butatriene structure ... 

The individual chain ends of the DC intermediates exhibit the same mesomeric structures (4) of the corresponding asymmetric carbenes AC and a carbon backbone with acetylene structure. It has been shown in a quantitative theory of the DC quintet states that the fine structure parameters Dq of all DC intermediates are... 

The determination of the photoluminescence parameters (excitation frequency, emission frequency, Stokes shift, fine structure parameter, and lifetime) can lead to information which, at the simplest level, indicates the presence of an electronically excited state of a species, but which can be sufficiently detailed so as to lead to a clear identification and characterization of the photoluminescent sites(J6-44). Moreover, measurements of the variations in the intensity and positions of the bands as a function of time (time-resolved photoluminescence) provide valuable kinetic data representing the reactions occurring at the surface. Although most of the photoluminescence measurements have been carried out at low temperatures for specific reasons (see Section III.C.2), there is much evidence that some of the excited states involved are present even at higher temperatures and that they play an important role in catalytic and photocatalytic reactions. Therefore, it is clear that the information obtained by photoluminescence techniques is useful and important lor the design of new catalysts and photocatalysts. 

Table 8 contains the values of ion-atom exchange interaction potentials for different atom fine states. Thus, the parentage coefficients are the same in this case as in the halogen case, and the fine structure parameter are identical to the case of positive oxygen atom. Because formula (22) contains the parameters of the atomic core, the exchange interaction potentials of Table 6 and 7 are different. 

D correspond to fine structure parameter and E to out-of axial symmetry... 

In principle, rotational constants and fine structure parameters of the predissociated state may also be affected by the predissociating state, as in the case of perturbations. Levels below the dissociation limit, which therefore cannot be predissociated, will also be shifted by their interaction with the continuum. In the case of strong predissociation, only this level shift affecting bound (sharp) levels will be seen, because the levels above the crossing point become too diffuse to be observed. This is the situation for the homogeneously predissociated Se2 B0+ (Atabek and Lefebvre, 1972) and NO G2 - states (Ben-Aryeh, 1973). 

Essentially similar results, as far as the chain length dependence of the fine structure parameters is concerned, have been found by Bennati et al. (1996a 1996b) for a series of thiophene oligomers with two to eight thiophene units (4 to 16 conjugated double... 

Tabic 2, Best fit fine-structure parameters for the complexes 11-13 and ll Py-l3 Py... 

The experimentally determined values for the zero-field splitting parameters, D = 3445 MHz and E = 865 MHz, are typical for the thpy ligand localized triplet state. Note that these values differ appreciably from those found above for the bpy ligand. Thus the values of the fine structure parameters also reflect that the triplet state is localized on the thpy ligand and not on the bpy ligand. Assuming that dipolar spin-spin interactions predominantly contribute to the... 

Here D denotes the axial fine structure parameter, whereas E describes the orthorhombic fine structure parameter [5]. The influence of an axial (i.e. D O and E=0) and an orthorhombic fine structure splitting (i.e. D O and E O) on a powder spectrum is shown in Fig. 3 for an isotropic g-tensor and for S equal to (e.g. Cr +). 

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