Thermal Broadening of the Mössbauer Line and of Narrow-Line Electronic Spectra in Solids

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Abstract
The dependence of the lattice vibration Hamiltonian upon the excitation state of an electron or nucleus is examined as a possible source of thermal broadening of narrow-line electronic spectra or Mössbauer spectra in solids. A simple model is proposed to illustrate this mechanism and calculational techniques described to determine the line width appropriate to that model. Application to the Mössbauer problem shows the absence of any observable thermal broadening except in the case of localized modes. The mechanism is consistent with the observed thermal broadening of the narrow lines of ruby, but that specific problem appears to be too complex to permit a detailed test of the theory.