Comment on "Effective field parameters in iron Mössbauer spectroscopy" [J. Chem. Phys. 47, 961 (1967)].

While the Mössbauer spectrum of a magnetically ordered powder sample can be used to determine the direction of the local hyperfine field (Bhf) in the coordinate system defined by the electric field gradient (efg) tensor, the spectrum of an oriented single-crystal provides a direct measurement of the angle between the absorbed or emitted γ and Bhf, primarily through the observed line intensities. Several solutions to the general static Mössbauer problem for M1 transitions (relevant for the two most commonly used Mössbauer isotopes: 57Fe and 119Sn) have been published,1–3 and all can be adapted to computer code to fit the relevant experimental variables. Unfortunately there is an error in Eq. (12) from Hoy and Chandra2 and both the sign of the last term and the sign of the exponent in the last term are incorrect. For single-crystal samples, this leads to a severe mis-calculation of line intensities when the angle (θ ) between Bhf and the principal axis of the efg tensor (Vzz) is non-zero, and so code based on this expression (see, for example, Ref. 4) gives incorrect fits. Starting from Eq. (11) of Hoy and Chandra2 for the intensity, I ( ei ↔ gj ), of the transition between the excited state, em, and ground state, g m: