Over the past two decades, the dipole approximation has facilitated a basic understanding of the photoionization process in atoms and molecules. Recent experiments on the 1s inner shells of small molecules at relatively low photon energies (⩽ 1000 eV) show strong nondipole effects. They are significant and measurable at energies close to threshold, in conflict with a common assumption that the dipole approximation is valid for photon energies below 1 keV.
Atomic, Molecular and Optical Physics | Physical Chemistry
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Lindle, D. W.,
Sellin, I. A.,
Mills, J. D.,
Sheehy, J. A.,
Langhoff, P. W.
Beyond the Dipole Approximation: Angular-Distribution Effects in the 1s Photoemission from Small Molecules.
AIP Conference Proceedings, 500