Observation of angular correlation between subsequently emitted Auger electrons

In an exploratory feasibility study we have measured the angular correlatio n between Auger electrons that were emitted in a cascadelike decay process after resonant photoexcitation, using synchrotron radiation from the Brookh aven National Synchrotron Light Source. While the monochromator was tuned t o the argon Is --> 4p resonance (3203.5 eV) we recorded Ar LMM Anger electr ons in coincidence with KL2,3L2,3,KL1L2,3, and KL2,3M1,2,3 Auger electrons. We found different nonisotropic angular correlations between distinct ener gy regions of the LMM group of Auger lines and the KL2,3L2,3 Auger electron s, while for other kinetic energies the LMM Auger electrons exhibit isotrop y. Because the KLL and LMM Auger energies are so different, we believe that the nonisotropic angular correlation observed is due to an alignment effec t rather than a dynamical postcollision interaction effect. [S1050-2947(99) 07801-4].