STATIONARY AND TIME-RESOLVED DYNAMIC NUCLEAR-POLARIZATION IN WEAK MAGNETIC-FIELDS IN THE PRESENCE OF DEGENERATE ELECTRON-EXCHANGE

The stationary and time-resolved dynamic nuclear Polarization (DNP) of diamagnetic reaction products in weak magnetic fields in the presence of degenerate electron exchange (DEE) has been investigated both expe rimentally and theoretically. The theoretical description of this effe ct, based on the solution of the Liouville equation for a spin density matrix of radical ions, has been suggested and compared with the desc ription based on the solution of phenomenological Bloch equations whic h had been proposed previously. An analytical expression for the depen dence of DNP on the delay time between the laser flash and the radiofr equency field pulse has been obtained within the Bloch model. The kine tics of DNP in the photolysis of perdeuteronaphthalene in the presence of fumaronitrile (trans-1,2-dicyanoethylene) at different rates of DE E has been investigated. The analysis and comparison of the theoretica l calculations and experimental data have shown that the decay of the kinetics is determined by the time of electron spin relaxation caused by DEE and the lifetime of radical ions. It has been shown that time-r esolved DNP can be applied to measure DEE rates and to investigate che mically induced dynamic electron polarization in weak magnetic fields.