ELECTRON-SPIN ECHO ENVELOPE MODULATION DUE TO EXCHANGE AND DIPOLAR INTERACTIONS IN A SPIN-CORRELATED RADICAL PAIR

The effects of exchange and electron-electron dipolar interactions on electron spin echo envelope modulation and free induction decay in a p hoto-induced spin-correlated radical pair are examined. Analytical exp ressions are derived for FID and spin echo signals as a two-dimensiona l function of the time intervals between the laser pulse and the micro wave pulses. It is predicted that these interactions can induce deep m odulation or oscillation on the out-of-phase spin echo envelope wherea s the in-phase echo vanishes. The modulation frequencies provide usefu l information for systems with small exchange and dipolar interactions even if the hyperfine inhomogeneity often produces unresolved spectra in cw EPR.