Temperature-Dependent Quadrupole Splitting in Paramagnetic S 2 Iron Compounds Example Deoxymyoglobin

2 Temperature-Dependent Quadrupole Splitting in Paramagnetic (S = 2) Iron Compounds (Example Deoxymyoglobin) 

3 Dynamically Induced Temperature-Dependence of Quadrupole Splitting (Example Oxymyoglohin) 

Originally, this temperature variation of AEq was attributed to the dynamic distribution of the terminal oxygen of the Fe02-moiety, as suggested by X-ray structural results for picket-fence porphyrins [26,27]. This view is now supported by NFS studies which provide more information on dynamic processes in iron-containing molecules. 

9 Nuclear Resonance Scattering Using Synchrotron Radiation 0 50 100 150 200 250 300 350 400 

The structural picture that was envisaged to represent the temperature-dependent fluctuations of the EFG tensor [15] is based on the X-ray structure of MbOa that exhibits a geometric disorder of Fe02 with two different positions of the terminal O-atom [28]. Within this stmcture, the projection of the 0-0 bond on the heme plane is rotated by about 40° in position 2 compared to 1 (Fig. 9.10). Conventional Mossbauer studies of single crystals of Mb02 have shown that the principal component of the FFG tensor lies in the heme plane and is oriented along the projection of the 0-0 bond onto this plane [29]. If the terminal O-atom is located in position 2, the EFG should be of the same magnitude as in position 1, but its orientation is different. The EFG fluctuates between positions 1 and 2 with a rate that depends on temperature. 

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