Selective excitation in pulsed EPR of a spin-correlated triplet-radical pair.
Experiments are described in which a low-amplitude microwave pulse excites only one out of three allowed transitions of the quinone radical (Q(A)(-)) in a spin-correlated triplet-radical pair 3PQ(A)(-) of the bacterial photosynthetic reaction center. A second high-amplitude pulse produces a FID whose temporal shape is strongly modulated with frequencies determined by electron-electron dipolar interaction in the pair. The FID is detected in both the in-phase and the out-of-phase channels. The out-of-phase FID is a result of switching off the magnetic dipolar interaction between 3P and Q(A)(-) due to decay of 3P during the time interval between the two pulses. Refocusing of FID by an additional non-selective pulse allows a dead-time free measurement of this modulation. The influence of the dead-time problem on the distance determination is discussed.
Kulik
L V
LV
Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, 630090 Novosibirsk, Russia. chemphy@ns.kinetics.nsc.ru
Borovykh
I V
IV
Gast
P
P
Dzuba
S A
SA
D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005583:Fourier Analysis; D008962:Models, Theoretical; D010788:Photosynthesis; D016992:Rhodobacter / Q000378:metabolism*