Rayleigh scattering from excited states of atoms and ions - art. no. 052714

Elastic photon scattering from the ground state and various excited states of carbon atoms and ions has been investigated, using the S-matrix formalis m, for incident photon energies ranging from 100 eV to 10 keV, contrasting the results obtained for different configurations. The excited states consi dered include hollow-atom states, where one or more inner shells are comple tely vacated. Ionic cases are considered as a limit of excitation. Results demonstrate how cross sections for different excited states group together according to shared properties of the configurations, such as the number of K electrons. Cross sections may exhibit deep dips below the K edge, depend ing on the occupation of the subshells corresponding to the strongest trans itions. Scattering from excited states can have significantly larger cross sections than scattering from the ground state, particularly just below the K resonance region, and therefore it needs to be considered in situations where there is a large population of these excited stares. Results are inte rpreted in terms of form-factor arguments and the qualitative behavior of i ndividual subshell amplitudes. The angular dependence of cross sections can be understood in terms of angle-dependent form factors and anomalous scatt ering factors, taken to be angle independent. Cases are identified for whic h excited-state total integrated cross sections are much larger than the co rresponding cross sections for scattering from the ground state. Our main r esults use an averaging over magnetic substates at the level of the amplitu de, exact only for fully filled subshells, but generally appropriate for th e carbon case considered, which simplifies the discussion and explains most of the general features. We also present results for a hollow lithium atom with and without this approximation to illustrate the differences that can arise in certain circumstances.