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A substantial difference in the angular distributions of 2p photoelectrons from polarized oxygen atoms was found for two antiparallel atomic polarizations. This magnetic dichroism was studied as a function of photon energy from 25 to 52 eV. Our method extends traditional photoelectron angular distribution measurements of open shell atoms to "complete" experiments in similar to spin-resolved measurements. The observed dichroism allows a determination of the dipole matrix elements for the es and ed photoelectrons and their phase difference including the sign. [S0031-9007(96)01267-7] PACS numbers: 32.80.Fb Photoionization and atomic collision processes can be completely described quantum mechanically by a limited number of amplitudes and their phase differences and thus the experiment from which the relevant amplitudes and phases can be extracted has been referred to as a "complete" experiment [1,2]. This possibility was first realized in the early electron-atom collision experiments of Eminyan et al. [3] and Standage and Kleinpoppen [4]. The first complete experiment in photoionization of atoms in the dipole approximation was reported by Heinzmann and co-workers [5,6], who measured the angular distribution and the spin polarization of photoelectrons for Xe 5p photoionization. The complete information in the latter experiment is obtained from the spin polarization of the photoelectron (providing up to three further parameters of the photoionization process besides the cross section and angular distribution). The first experiment of this kind was followed by a series of further studies with a main emphasis on rare gas atoms. A complementary method for complete atomic photoionization experiments employs the polarization of the target atoms. The sensitivity of this method to additional photoionization parameters depends on the target preparation instead of the detection sensitivity to spin polarization. We refer for this class of experiments to the work of Klar and Kleinpoppen concerning the complete analysis of the relevant amplitudes and phases [7]. Successful experiments using polarized targets have first been reported [8-11] using laser excitation for the preparation of the initial state. However, these experiments focused predominantly on resonant photoionization processes where the information on matrix elements and phases is largely reduced. An alternative approach to such a complete analysis of nonresonant photoionization has been reported by Hausmann et al. [12] and Becker [13]; in their photoionization experiments on atomic magnesium and argon the angular distributions of the photoelectrons and Auger electrons provide the angular distribution asymmetry parameter b and the alignment parameter A 20 . These quantities together with the partial photoionization cross section s make it possible to derive matrix elements for continuum s and d electrons and the cosine of their relative phase. Related experiments employ the polarization of the fluorescence radiation instead of the angular distribution of the Auger ele...

A study of the photoionization of atomic calcium in the region of the 3p 5 3d4s 2 1 P 1 resonance at 31.41 eV is described. Measurements are made of the photoelectron angular distributions and branching ratios, corresponding to the case where the Ca + ion is left in excited Rydberg levels converging to the ground level of the doubly charged ion. The data are used to examine the validity of LS coupling and the spectator model of resonant Auger decay.