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Double Excitation Of Helium By Fast Particles Of Charge Z, James H. Mcguire, Jack C. Straton
Double Excitation Of Helium By Fast Particles Of Charge Z, James H. Mcguire, Jack C. Straton
Physics Faculty Publications and Presentations
Results of calculations of double excitation of helium to n=2 states for fast projectiles of charge Z are presented. Nonzero Z3 contributions for single and double excitation occur only when time-ordering contributions from the second-order amplitude are nonzero. For double excitation, electron correlation must also be nonzero to obtain Z3 terms. The time-ordering effects arise from virtual off-energy-shell intermediate states. As with second-order amplitudes for Thomas singularities in electron capture, the energy-nonconserving amplitude is connected to the second-order energy-conserving amplitude by a dispersion relation. Comparison is made with experiment.