Scattering asymmetry, polarization

E.E.Nikitin, Azimuthal asymmetry in scattering of polarized atoms in the P-state, Khim. Fiz. 4, 310 (1985)... 

E.I.Dashevskaya and E.E.Nikitin, Scattering asymmetry for atoms of helicopter polarization manifestation of slipping, Optika i Spectr. 68, 1006 (1990)... 

The asymmetry parameter, which was defined in Section 3.4 as the average cosine of the scattering angle, depends, in general, on the polarization state of the incident light. However, the asymmetry parameter for a spherical particle is clearly independent of polarization and is given by... 

Figure 18 Steric asymmetries R plotted in a polar plot for NO scattering from Ru(0001)-(1 x 1)H, Ag(l 1 1) and Pt(l 1 1). The radius of the polar plot denotes the value of R( f). The R( f) scale is —0.2 to 0.2 for the first two plots and —0.2 to 0.8 for Pt(l 1 1). The thick circle in the plots denotes R(0f) = 0. The incidence angles are respectively i = 60°, 62°, and 50°, with energies Ei % 0.25 eV. For Ag(l 1 1) data for E[ = 0.44 eV. is shown by the filled diamonds. These additional data are given in order to better see the trend of R( f) as a function of 0f. Lines drawn through the data points are to guide the eye. From Berenbak et al. [149].

Au photoelectrons are spin polarized due to the high spin-orbit coupling of the metal. Therefore, an alternative mechanism for the transmission asymmetry obseved in [36] could be based on changes in the photoelectron spin angular momentum. We do not attribute the yield asymmetry to spin polarization because the stearoyl-lysine monolayers in [36] contain only low atomic number atoms that do not scatter spin. 

Campbell and Farago [89, 90]. They reported 0.5% asymmetry in the scattering of 5 eV polarized electrons from camphor. Calculations stimulated by these results pointed out the importance of shape resonances [91] and temporary negative-ion states [92] in the scattering process. 

Finally, in a recent paper, Yeganeh et al. suggest that the large asymmetries seen in polarized electron transmission are partly due to a combination of the presence of a molecule with axial chirality, surface orientation, and cooperative effects in the monolayer [129]. They use scattering theory to show that differences in transmitted intensity arise from the preferential transmission of electrons whose polarization is oriented in the same direction as the sense of advance of the helix. 

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. 

However if one scatters the partially polarized beam again at angle 2. s shown in Fig. 12, one will observe an asymmetry in the number of particles scattered. The asymmetry manifests itself as a difference in the counting rates observed at angles 2 2 second scattering is in the same plane as... 

The inner valence orbital 4ai is a bonding combination of P3s and His. The P3s character was experimentally confirmed by the behavior of the angular distribution (asymmetry) parameter p for photoionization [6 to 8]. Significant P3s-H1 s overlap was found in several theoretical calculations ab initio SCF-MO [9], SCF-Xa-SW (scattered wave) [10], SCM (self-consistent multi-polar)-Xa-DV (discrete variational) [11]. A participation of P3p in 4ai was, however, assumed in the early MO picture of Walsh [4] and was supported in an interpretation [12] of earlier SCF-MO results [13] by a localized orbital picture. 

---