Photoion alignment

In photoionization, analogous to photodissociation, the photofragment, here the photoion, can be aligned. The alignment of the photoion, (Greene and 

1982) may be measured if the molecular photoion is produced in a fluorescing excited electronic state. The polarization of the fluorescence determines the alignment of the nascent photoion. The alignment of the J+ photoion rotational level is defined as 

Kinematic constraints for photoionization of a linear molecule limit the alignment parameter to the range 

In the high-J+ limit, the value of is directly determined from the fluorescence polarization, P, 

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Photoelectron Angular Distribution, Photoion Alignment, and Spin Polarization. 595... 

Formally, alignment and orientation follow from the general symmetry properties of statistical tensors pkK introduced in Section 8.4. Spherical symmetry leads to k = k = 0, axial symmetry to k — 0, and alignment requires k = even, and orientation k = odd. Since the dipole approximation in the photoionization process restricts k to k < 2, a photoionized axially symmetric state can only have Poo, p10, and p20 Poo describes isotropy, and the alignment is given by [BKa77]... 

Hence, the emission of Lj-MjMj Auger electrons is isotropic, while that of Auger electrons has an angular distribution coefficient proportional to the alignment parameter. Therefore, a measurement of (Lj-N Mj) is equivalent to a determination of the alignment of the photoionized state, and this quantity can be included in the list of observables in 2p photoionization of magnesium. 

Introducing normalized parameters, namely, the Auger decay parameter ak and the angle-dependent alignment tensor s kK Jk, 0 Ox) of the photoionized intermediate hole-state J, both defined for k — even and k < 2[Pg.356]

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