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Title: 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 X-ray 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 origin-dependent expression for the oscillator strength. The oscillator strength can be made origin-independent 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 origin-dependent expression may violate the Thomas-Reiche-Kuhn sum rule and the origin-independent expression can result in negative transition probabilities.
Authors:
; ;  [1]
  1. 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; E1-TRANSITIONS; ELECTRIC DIPOLES; MAGNETIC DIPOLES; OSCILLATOR STRENGTHS; POTENTIALS; PROBABILITY; QUANTUM MECHANICS; SPECTROSCOPY; SUM RULES; VECTORS; VISIBLE RADIATION; WAVE PROPAGATION; WAVELENGTHS; X RADIATION