An expression for the amplitude of a pulse of synchrotron radiation (SR) coherently scattered in forward direction by a randomly oriented Mössbauer absorber is derived from the theory of γ optics. It is assumed that the hyperfine splittings present in the Mössbauer nuclei can be described in the framework of the spin-Hamiltonian formalism. In the general case of a thick Mössbauer sample, which consists of randomly oriented paramagnetic iron-containing molecules (for example, a frozen solution of a ${}^{57}\mathrm{Fe}$ protein) in an applied magnetic field, the response of this sample on an incident monochromatic and fully polarized SR beam cannot be given analytically because of the integrations involved. The way to evaluate nuclear forward-scattering spectra for this general case numerically is outlined and results of calculations with a corresponding program package called SYNFOS are shown and compared with experimental results obtained by measurements of the high-spin iron (II) “picket-fence” porphyrin $[{\mathrm{F}\mathrm{e}(\mathrm{C}\mathrm{H}}_3{\mathrm{C}\mathrm{O}\mathrm{O})\mathrm{T}\mathrm{P}}_{\mathrm{piv}}\mathrm{P}{]}^{-}$ in an applied field of 6 T.

• Received 14 July 1997

DOI:https://doi.org/10.1103/PhysRevB.56.14082