M.C.D./M.C.P.L. saturation theory with application to molecules in D_∞h and its subgroups

Abstract

The M.C.D. of a system with a paramagnetic ground state will deviate from simple H/T dependence at sufficiently high field and/or low temperature, and this deviation is referred to as a saturation effect. A detailed theoretical discussion of this phenomenon is presented, and specific application is made to molecules in point group D _∞h and in its subgroups down through C ₃. A single general formula is found to apply in all cases to an allowed electronic transition between two ‘isolated’ electronic states. The properties and applications of this formula are described in some detail. The formula is then generalized to apply to saturation behaviour for the corresponding emission phenomenon, magnetic circularly polarized luminescence (M.C.P.L.), where the additional effect of photoselection must be considered. A saturation analysis in M.C.D. is also presented for one special case of accidental degeneracy, that for a ²P_3/2 ‘atomic’ ground state in a linear molecule. Various experimental considerations in saturation work are also discussed, and a method is presented for correcting for the effect of magnet reluctance when a large superconducting solenoid is used. Corrections may easily be made for the presence of B terms.