Manifestation of spin-orbit interactions in photoemission from free atoms

Fine-structure resolved electron spectrometry in conjunction with highly resolved synchrotron radiation have been used to observe in detail some of the consequences of the spin-orbit interaction on the decay of the Ar 3s → np autoionizing resonances. The findings include (a) a 20% enhancement in the ratio of the partial cross-sections for the isolated 6p single-electron excitation, (b) the presence of a previously unidentified two-electron excitation in the vicinity of the 8p resonance, and (c) different resonance widths in σtot, σ3/2, and σ1/2 for the 10p excitation, namely, 1.64 meV, 1.9 meV, and 1.0 meV, respectively. These data, and the experimental capabilities they reflect, highlight the importance of the spin-orbit interaction in determining the dynamics of photoemission from free atoms.