Experimental Identification of Specific Spin-Orbit Coupling Mechanisms During Photoionization

Recent fluorescence polarimetry experiments have shown that even with a relatively light target like Ar, large relativistic effects are surprisingly common in photoionization. We show how dynamic magnetic effects during photoionization can be specifically identified as target spin-orbit coupling, target spin-continuum orbit coupling, or continuum spin-orbit coupling, the latter being the Fano effect. Our analysis involves the extraction of partial-wave cross sections from experimental polarization measurements for excited residual ion fluorescence. We demonstrate the application of this technique for fluorescence from the fine-structure resolved states of $Ar^+\,3p^4\,\left[ {{ }^3P} \right]\;4p\,{ }^2D_{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2} ,\,{ }^4P_{5 \mathord{\left/ {\vphantom {5 2}} \right. \kern-\nulldelimiterspace} 2} ,\,{ }^4D_{5 \mathord{\left/ {\vphantom {5 2}} \right. \kern-\nulldelimiterspace} 2} $. Support provided by the NSF (Grants PHY-0354946 and PHY-0098545) and the DOE (LBNL/ALS)