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Paramagnetic Resonance and Hyperfine Structure in the Iron Transition Group

may be observable in polar semiconductors. Unfortunately AEt has been computed' only at T=00, so that the form of the de- pendence of the effective gap width on temperature is not known. The situation seems somewhat more hopeful in the case of optical excitation. The frequency of maximum absorption will be Aw=EG-2AEo. It will be noted that the effective energy shift AEo here differs from AEt, for the energy shift AEt includes a contribution from the alteration of the form of the phonon; but, by the Franck-Condon principle, this contribution is absent in an optical process. Thus AEo must be computed by finding the change in energy of an electron in the field of a phonon, assuming the phonon states to be unaffected by the presence of the electron. Using the methods employed in the treatment of electrical break- down in polar crystals,2 we have computed3 AEo as a function of temperature (wt is restrahl frequency, eo and s, are optical and static dielectric constants): (AE43= me4wt2Q)( 1 i)( exphotEi )2l ( hte h iE)1-2 It may be hoped that the polaron effect can thus be observed as a dependence of the frequency of maximum absorption X on http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review American Physical Society (APS)

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