Spin Polarization and Spin - Lattice Relaxation In the Lowest Triplet State of Pyrazlne

The different mechanisms proposed for the spin lattice relaxation process of a paramagnetic impurity in ionic crystals are briefly summarized. The decay characteristics of the pyrazine phosphorescence in cyclohexane and benzene matrices at 1.6K and its temperature dependence can best be explained if competition between the spin lattice relaxation process between the triplet sublevels and the radiative process from one of the « -if sublevels of pyrazine is invoked. Spin polarization in the B-' state of pyrazine at 1.6K is achieved by the selection rules imposed on the 1 n TT 1 TT TT intersystem crossing process, B ' —^ i' ( v^» followed by the fast internal conversion process B ' (T ) «~> B ' ( T ). The latter sublevel (T ) of the B ' state is the emitting sublevel. This scheme is y lu found to explain the observed temperature effects on the decay characteristics as well as the unique phosphorescence polarizauion along the N...N axis of the pyrazine molecule. Limits on the spin lattice relaxation time (T.), on the lifetime of the T,—^S radiationless process and on the radiative lifetime of phosphorescence from theT andT sublevels of the B»' state of pyrazine at 1.6K are dotermined. Th3 effect of the magnetic field on the decay curve is demonstrated, and briefly described.