Examples of relaxation phenomena in Mossbauer spectra

In this section examples of observed Mossbauer spectra are presented which illustrate the concepts discussed above. The analysis which will be used requires a slight generalisation of the expression given in Equation (5.22). 

The two frequencies coj and coj between which the system relaxes, were originally assumed to occur with the same probability. However, it is more realistic to assign to them probabilities Pi and pj which may be unequal. In this case the lineshape can be shown to be given by 

Naturally when a = 0 Equation (5.32) reduces to Equation (5.22). The static limit (oJr=0) of Equation (5.32) is given by 

In contrast to the situation represented by Equation (5.25) there are now two lines with unequal intensities proportional to pj and P2 respectively. On the other hand, in the rapid dynamic limit (i.e. cur Am) Equation (5.32) 

Therefore in the extreme motional narrowing regime (i.e. cor - oo) the spectrum collapses into a single line which is centred not at cu but at c5 + a Aft). 

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