A generalization of methods for determining g tensors

Schonland ambiguity in the electron nuclear double resonance analysis of hyperfine interactions: Principles and practice

“…Hence, one may wonder if for a corresponding set of experimental data an analogous Schonland-type ambiguity in the best-fit solution exists. This problem has, to the best of our knowledge, neither been treated yet from a theoretical nor from a practical viewpoint in the literature, although it has been recognised that in the analysis of EPR spectra, treating the HF interaction as a perturbation to first order, the ambiguity does arise [3][4][5]. Our interest in this matter, and particularly in the ENDOR analysis, arises from our study of the structure of radiation-induced radicals in single crystals of mono-and disaccharides [6][7][8][9] and other bio-organic molecules [10][11][12][13].…”

“…[3,4]) have extended the work of Schonland and further documented possible ambiguities in fitting results. Nonetheless, in experimental EPR literature, this problem is often not recognised.…”

“…(3) or (6), related to the sense of rotation in the three planes. Labelling the a, b and c parameters with 3 for rotation in the {ab} plane, with 1 for {bc (*) } and with 2 for {c (*) a}, one finds (see Ref.…”

“…a, b and c (being expressed also by the elements of the squared g $ tensor) can directly be calculated from the maximum and minimum g value encountered in this plane, and the angle h at which the maximum g value occurs [1,3]. Ignoring for the moment the possible presence of symmetry-related centres (site splitting), whose g $ tensors are related to those of the ''original" centre by the symmetry operations of the crystal's point group [4], the occurrence of two best-fit solutions springs from an ambiguity in the positive rotation sense in the planes, thus in the sign of h or, alternatively, in the sign of c. Indeed from Eq.…”

EPR study of SO4− radicals in K4LiH3(SO4)4 crystals

“…A flow of cold nitrogen vapour was used for taking the spectra between 77 K and RT with the accuracy of the temperature setting of i l K. To evaluate the g-tensors of the sulphate radicals a right-handed, orthogonal reference system was assumed with the z-axis parallel t o the tetragonal axis while the xand y-axes were parallel to the respective edges of the monocrystal. The principal values J. MINGE and T. KRAJEWSKI and direction cosines of the g2-tensor were determined from the rotation patterns observed in the yz, zx, and xy planes using a computer program based on the standard methods [5,6]. Because of the ambiguity of choice between four curves in each plane (belonging to the crystallographically equivalent, but magnetically non-equivalent centres), which leads to the two different sets of the g-tensor principal values, the additional rotations of the sample were performed to find the maximum g-value.…”