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 measu rements of the linear dichroism in absorption-detected magnetic resonance ( LD-AMDR) causes an experimental error in determining the angles of the trip let spin-sublevel axes relative to the optical dipole transition moment tha t can be be as large as 20 degrees. We have obtained an analytical correcti on for this error. The error analysis was applied to LD-ADMR experiments on the carotenoidless mutant R26 of Rhodobacter (Rb.) sphaeroides. The correc ted angles of the triplet x- and y-axis with respect to the optical transit ion dipole moment at 896 nm of R26 are 86 degrees +/- 4 degrees and 22 degr ees +/- 3 degrees, respectively. (C) 1999 Elsevier Science B.V. All rights reserved.