The consequences of improperly describing oscillator strengths beyond the electric dipole approximation
The interaction between a quantum mechanical system and plane wave light is usually modeled within the electric dipole approximation. This assumes that the intensity of the incident field is constant over the length of the system and transition probabilities are described in terms of the electric dipole transition moment. For short wavelength spectroscopies, such as Xray absorption, the electric dipole approximation often breaks down. Higher order multipoles are then included to describe transition probabilities. The square of the magnetic dipole and electric quadrupole are often included, but this results in an origindependent expression for the oscillator strength. The oscillator strength can be made originindependent if all terms through the same order in the wave vector are retained. We will show the consequences and potential pitfalls of using either of these two expressions. It is shown that the origindependent expression may violate the ThomasReicheKuhn sum rule and the originindependent expression can result in negative transition probabilities.
 Authors:

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 Department of Chemistry, University of Washington, Seattle, Washington 98195 (United States)
 Publication Date:
 OSTI Identifier:
 22493338
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 23; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION; APPROXIMATIONS; E1TRANSITIONS; ELECTRIC DIPOLES; MAGNETIC DIPOLES; OSCILLATOR STRENGTHS; POTENTIALS; PROBABILITY; QUANTUM MECHANICS; SPECTROSCOPY; SUM RULES; VECTORS; VISIBLE RADIATION; WAVE PROPAGATION; WAVELENGTHS; X RADIATION