Asymmetry fine-structure

The latter equation assumes a 100% linearly polarized ionizing radiation, a is the fine structure constant, Nni is the number of electrons in a nl subshell, Dni->ei l is a radial dipole photoionization amplitude, fini is the dipole photoelectron angular asymmetry parameter, and A i2 is the electric dipole-quadrupole interference term arising due to the correction term ikr in the above expression for Mab,... 

The existence of the fine-structure effect has been demonstrated for sodium (Hanne, Szmytkowski and van der Wiel, 1982 McClelland et ai, 1985 Nickich et al, 1990) using the time-reversed arrangement. A polarised electron beam is superelastically scattered from sodium atoms excited to 3 P /2 or 3 3/2 states by a single-frequency laser. McClelland et al. (1985) measured the spin asymmetry of polarised electrons that de-excite unpolarised atoms from the 3> P3/2 fine-structure state over the angular range —35° < 6 < 35°. As expected from reflection symmetry, the... 

The fine structure is due to sequences of three double bonds ccc, cct,tct etc. and the asymmetry in the HT and TH triplets is a consequence of the absence of cis HH structures. The all-cis polymer, made with ReCls as catalyst, has no choice but to be fully biased (3,12). Cis HH structures do not form because of the severe steric... 

Finally, there is a pressing need for more-detailed information on the molecular fine-structure, or conformation, of polysaccharides in solution. The potential of small-angle x-ray diffraction for distinguishing between a random coil and a broken or partial helix in solution has been established. A better definition of the helical conformation of dissolved polysaccharides, which, because of basic chemical asymmetry, have a favored chirality ( handedness ), is awaited. This area of x-ray study is only beginning to be developed. ... 

The first prerequisite for measurement of photoelectron spin-polarization is the ability to separately detect the photoelectrons ejected from the different fine-structure levels (e.g., 2n3/2 and 2n1/2 for HX+ X2n). When the molecule contains a heavy atom (e.g., large spin-orbit splitting), it becomes easier to use the electron kinetic energy to distinguish the photoelectrons ejected from the different fine structure channels. For spin-polarization analysis, the accelerated electron beam (20-120 keV) can be scattered by a thin gold foil in a Mott-detector. The spin-polarization is determined from the left-right (or up-down) asymmetry in the intensities of the scattered electrons (Heinzmann, 1978). Spin polarization experiments, however, are difficult because the differential spin-up/spin-down flux of photoelectrons is typically one thousandth that obtained when recording a total photoionization spectrum. 

Similarly to the angular asymmetry parameter, / , the spin-polarization parameters have signed values and their expressions, as function of contributing transition moments, in principle permit determination of the relative signs of these transition moments. However, in contrast to the situation for atoms, the number of relevant unknown parameters exceeds the number of experimentally measurable quantities. Nevertheless, measurement of both resonance widths and spin-polarization parameters can considerably narrow the assignment possibilities. This is particularly true in the region between the two ion-core fine-structure thresholds, for example, 2n3/2 and 2n1/2 of an AB+ 2n state. 

The fine structure constant A was determined indirectly from the perturbations by the riy state of the observed Zeeman shifts in the state, A= -177.3 5.6 cm" [2]. A splitting of 160 30 cm was derived from an asymmetry of the vibrational components of three photoelectron bands [1]. A = ( )188cm was calculated from the atomic spin-orbit coupling constants and from the F hyperfine coupling constant [2]. The method used was described in... 

An asymmetry, called vibrational fine structure and attributed to C—H vibrational excitation, is observable on C Is spectra recorded on polymers containing saturated hydrocarbon components as polyethylene. ... 

The fine structure interaction involves the interaction between the magnetic dipole moments of electrons on an atom containing more than one unpaired electron. The magnitude of this interae-tion is described by the second rank D tensor. Second-order terms, D and EID correspond to the axial zero field splitting (Z)) and the asymmetry parameter EID, which varies from 0 (axial symmetry) to 1/3 (rhombic symmetry) (S.D.S). Fourth- and sixth-order corrections to the fine structure interaction tensor D may also be necessary to adequately interpret the spectrum,... 

Langmuir-Blodgett (LB) technique has been also used for the preparation of Pc-based OFET, as it allows the fine control of both the structure and the thickness of the film at the molecular level [226,227], OFET devices based on amphiphilic tris(phthalocyaninato) rare earth, triple-decker complexes have been prepared by LB technique, showing good OFET performances [228], More recently, ambipolar transport has also been realized in OFET devices through a combination of holeconducting CuPc and n-conducting Cgo fullerene, in which the asymmetry of the... 

The function of photosynthetic bacterial reaction centers (RCs) is closely related to their structure. In the last 15 years a wealth of structural data has been accumulated on bacterial RCs, mainly through X-ray structure analysis of three-dimensional RC crystals. In this chapter, the arrangement of protein subunits and cofactors in the RC complexes ofthe non-sulfur purple bucienn Rhodobacter (Rb.) sphaeraides mARhodopseudomonas (Rp.) viridis are delineated. A prominent feature ofthe bacterial RCs is their location in the photosynthetic membrane. Inside the RC complex, a finely tuned arrangement of amino acid residues and cofactors maintains a highly ordered system. The positions and likely functions of hydrogen bonds are described, since they play a key role in protein-cofactor interactions. Special emphasis is placed on the symmetry relations in the RC and on the functional asymmetry of electron and proton transfer that contradicts the observed pseudo two-fold structural symmetry. 

TEM studies of thin transverse fiber sections show that the cortical structure of cashmere is considerably different from that of fine wool [296,311,320]. Australian and Chinese cash-mere fibers display both bilateral symmetry and random cell arrangements, not only in cashmere fibers from different samples but also in fibers from the same fleece [296,311], whereas fine wool fiber exhibits bilateral asymmetry only. The variation in cortical structure among fibers from the same cashmere fleece suggests that different mechanisms may be involved in fiber formation. Cashmere cortex is composed predominantly of ortholike and mesolike cells, whereas fine wool is composed predominantly of ortho- and paracortical cells arranged bilaterally. Because of the variations observed, many transverse sections need to be examined before definitive statements can be made about the physical structure of fiber from a given cashmere sample. 

The two bands have a similar fine-line structure in the regions where the effects of asymmetry are small, that is, for large K values. Where the effects of asymmetry are important, the selection rules... 

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