TRANSIENT EPR OF WEAKLY COUPLED SPIN-CORRELATED RADICAL PAIRS IN PHOTOSYNTHETIC REACTION CENTERS - INCREASED SPECTRAL RESOLUTION FROM NUTATION ANALYSIS

Transient EPR signals at high microwave power are calculated for a weakly coupled, spin-correlated radical pair and compared to experimental results obtained for photosystem I in fully deuterated Synechococcus lividus. It is shown that the observed phase effects in the transient nutations result from the coupling between the spins in the radical pair P700+Q-. The spectral variation of the nutation frequency leads to an effective increase in the spectral resolution and is used to show that the principal x axis of the g tensor of Q- is roughly parallel to the symmetry axis of the pair dipole coupling tensor, a conclusion reached previously from the simulation of the spin-polarized spectrum.