Moessbauer relaxation spectra in arbitrarily ordered absorbers - line shape analysis for an iron(II) spin-crossover complex in the presence of texture

The stochastic theory of Moessbauer line shapes is formulated in a fashion which allows the evaluation of the spectral shapes for absorbers of arbitrary thickness, texture, and an anisotropic Lamb-Moessbauer factor. The results are specialized to a two-state-relaxation model of fluctuating electric hyperfine interaction in the case of an absorber of axially symmetric texture. The formalism is applied to the line shape analysis of Moessbauer spectra of a textured sample of the spin-crossover complex [Fe(mtz)6](PF6)2 (mtz = 1-methyltetrazole). It is found that between 185 and 240 K the rate constants for the HS → LS conversion are temperature independent, whereas an Arrhenius behaviour is found for the LS → HS conversion