Spin polarization of Auger- and of photoelectrons from barium atoms exposed to circularly polarized radiation and their cross comparison

New results of spin polarization of both photoelectrons and Auger electrons are reported after 5p photoionization of free Ba atoms with circularly polarized light. A substantial polarization transfer from the spin polarized photons to the spin polarized photoelectrons and via the hole state orientation to the spin polarized Auger-electrons is observed. The cross comparison of the results for photoelectrons and Auger-electrons allows a quantitative test of the assumed two step model where both electron-emission processes occur in sequence. PACS32.80.Fb; 32.80.Hd Creation of vacancies in inner atomic shells by photon or particle impact often gives rise to subsequent Auger decay. Recently, these Auger electrons have been measured to be strongly spin polarized for the electron spectroscopy studies with free barium atoms [1] and Rb-adsorbates [2], where the primary photoemission process has been performed by means of spin polarized i.e. circularly polarized radiation. In their emission characteristics these Auger electrons reflect a non-statistical population of the magnetic substates of the intermediate ionic state produced by the spin oriented initial impact [3, 4]. Consequently, an orientation of the intermediate state can be transferred partially to the Auger electron spin polarization [5, 6]. On the other hand the data of spinand angle resolved Auger spectroscopy can be used to determine alignment and orientation of the intermediate photoion state from the experiment [ 1 ]. Cross comparison of these results with the corresponding dynamical parameters characterizing the primary photoelectron emission process, angular distribution and spin polarization parameters which form a "complete experiment", should answer whether photoelectron and Auger electron emission are subsequent processes in a two-step model or whether they have to be seen as a dynamical combination. A mutual influence of Augerand photoelectrons would give rise to the so-called post-collision interaction, indicating a break-down of the two-step model. A reference case is the 4 d ionization of xenon [7] for which both the occurrence [8] and the vanishing [9] of postcollision interaction was discussed in detail. Figure 1 shows the angle-resolved measurement [1] of the spin-polarization component A (O) (parallel to the photon beam) of Auger electrons in the 03P1Pa(1So) Auger line of Ba atoms in photoionization using circularly polarized synchrotron radiation from the 6.5 m N.I. Monochromator (A,~ = 0.18 nm FWHM) at BESSY [ 10]. For Auger electrons the angular distribution of the polarization component A (O) has the same analytical form as for photoelectrons [10]: A eP2 (cos O) A(O)=y 1 (fl/2)-P2 (cos O) with the second Legendre polynomial P2 (cos O) and the light helicity ? but with different dynamical parameters for the angular distribution of the spin polarization. Since the photoelectrons in the example [ 1 ] of Fig. 1 were too slow ( < 1 eV) to be analyzed, we had to repeat the experiment at photon energies higher than 23.5 eV in order