Photoelectrons angular distribution parameter

In this equation, the spherical angles 6 and

defined relative to the photon momentum k, photoelectron momentum p, and photon polarization vector e, as indicated in Figure 1, fi i is a dipole photoelectron angular distribution parameter, yni and Sni are nondipole photoelectron angular distribution parameters. 

Both models demonstrate sizable oscillations, i.e., confinement resonances, in the energy dependence of photoelectron angular distribution parameters. The resonances fade away rapidly with an increasing energy of the photoelectrons. The decrease in the resonance amplitudes with increasing... 

The discovery of confinement resonances in the photoelectron angular distribution parameters from encaged atoms may shed light [36] on the origin of anomalously high values of the nondipole asymmetry parameters observed in diatomic molecules [62]. Following [36], consider photoionization of an inner subshell of the atom A in a diatomic molecule AB in the gas phase, i.e., with random orientation of the molecular axis relative to the polarization vector of the radiation. The atom B remains neutral in this process and is arbitrarily located on the sphere with its center at the nucleus of the atom A with radius equal to the interatomic distance in this molecule. To the lowest order, the effect of the atom B on the photoionization parameters can be approximated by the introduction of a spherically symmetric potential that represents the atom B smeared over... 

Figure 27 Relativistic RPAE calculated results [30] of the 6s dipole photoelectron angular distribution parameter j06s(eo) from free Hg and <3>Hg, The RRPA calculations included interchannel coupling...

Figure 28 Relativistic RPAE calculated results [30] of the 6s dipole photoelectron angular distribution parameter of Hg at two different levels of truncation with regard to RRPA interchannel coupling (a) including channels from the 6s2 subshell alone, Aa, and (b) including channels from the 6s2 and 5d10 subshells of d>Hg, as in Figure 27. Confinement effects were accounted for in the A-potential model at the frozen-cage approximation level.

A detailed derivation of the photoionization differential cross-section expression, leading ultimately to the angular distribution in Eq. (4), is provided in Appendix A. This will help provide a detailed understanding of the photoelectron dynamics that determine the angular distribution parameters, as will be discussed in a subsequent section, but for now it may help develop the reader s appreciation of this phenomenon to provide a simple, if necessarily inexact, mechanical analogy. 

Figure 2.13 Theoretical values for the partial cross section

In Figs. 5.8 and 5.9 the angular distribution parameters / 2p, / (L3-M1M1) and /ffLj-MjMj) are shown as a function of the photon energy. Within experimental error, (Lj-MjMj) is zero as predicted by theory, and this underlines the quality of the experimental data. The angular distribution of photoelectrons cannot be measured closer to the 2p ionization threshold than approximately 2.4 eV, because... 

Angular distribution parameters ft of photoelectrons Is photoionization in helium / = 2.0 (in dipole approximation)... 

Dubs, R.L., Dixit, S.N. and McKoy, V. (1986). Extraction of alignment parameters from circular dichroic photoelectron angular distribution (CDAD) measurements, J. Chem. Phys., 85, 6267-6269. 

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