Mössbauer investigation of deoxymyoglobin in a high magnetic field. Orientation of the electric field gradient and magnetic tensors

Abstract

We have examined the Mössbauer spectra of deoxymyoglobin in a 6 T magnetic field in the temperature range 4.2–195 K. Spectra were fitted by the least-squares method using a phenomenological model in which the internal magnetic hyperfine field was assumed to be related to the applied field by a temperature dependent tensor ω̃. The results indicate that ω̃ has axial symmetry and a principal axis system aligned with that of the electric field gradient (efg). The principal component of the latter is negative and lies on the symmetry axis of ω̃. Our fits indicate that the efg asymmetry parameter is η = 0.7, with no appreciable temperature dependence. Both axial and transverse components of ω̃ have the expected 1/T temperature dependence for T > 20 K. Our experimentally determined value of η, combined with published single crystal zero-field measurements, constrains the efg-heme relative orientation to two possibilities. In neither of these is an efg principal axis near to the heme normal.