Optical detection of magnetic circular dichroism (ODMCD) for the zero-field microwave transitions of the triplet state

Magnetic circular dichroism is detected in the magnetic dipole transitions between the sublevels of photoexcited triplets at 1.6°K utilizing optical detection methods. The theoretical and experimental magnitude of the effect are in excellent agreement. It is demonstrated that when the g factor is positive, a transition which increases in frequency with increasing field will be left-handed circularly polarized while a transition which decreases in frequency with increasing field will be right-handed circularly polarized. The sign of the g factor is determined for the triplet state of several substituted benzenes and is found to be positive in all cases. It is also shown that optical detection of MCD of the triplet state can give the sign of the g factor and the relative order of the zero-field levels but not the absolute order unless it is coupled with the determination of whether the interaction with the microwave field leads to stimulated absorption or stimulated emission processes.