Linear dichroism in triplet–singlet difference spectra of photosynthetic pigment–protein complexes, monitored with absorbance-detected magnetic resonance: correction for non-ideal optical effects

The non-sinusoidal modulation of the photo-elastic modulator used for measurements of the linear dichroism in absorption-detected magnetic resonance (LD-AMDR) causes an experimental error in determining the angles of the triplet spin-sublevel axes relative to the optical dipole transition moment that can be be as large as 20°. We have obtained an analytical correction for this error. The error analysis was applied to LD-ADMR experiments on the carotenoidless mutant R26 of Rhodobacter (Rb.) sphaeroides. The corrected angles of the triplet x- and y-axis with respect to the optical transition dipole moment at 896 nm of R26 are 86°±4° and 22°±3°, respectively.