Vanishing radiative widths

Fig. 8.22. The vanishing radiative width in the Ba spectrum. Experimental data are shown which correspond to oscillator strength measurements below the ionisation threshold by the magneto-optical method described in chapter 4, which also gives an overview of the Ba spectrum including the broad 5d8p perturber responsible for the vanishing radiative width. The inset shows a comparison between measured values (squares) and an MQDT extrapolation (triangles) on a logarithmic scale (see also fig. 4.3 - after J.-P. Connerade et al. [136]).

If the retarded interaction is ignored and the operator Hmt is removed from the total Hamiltonian (4.2), then the operator H becomes a sum of two independent Hamiltonians, one of them (Hi) describing the crystal elementary excitations - those which occur when the retardation effects are ignored and the second (H2) giving the elementary excitations - transverse photons in vacuum. The presence of the operator H3 leads to the interaction between carriers with the transverse electromagnetic field. In the case of an atomic gas this interaction causes, in particular, the so-called radiative width of energetic levels of excited states. In the case of an infinite crystal possessing translational symmetry the radiative width of excitonic states vanishes.29... 

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