A theoretical analysis of quantum mechanical mixing of spin 1/2 with spin 3/2 and admixed spin 3/2-5/2 states in ferric haem complexes

The quantum mechanical admixture of spin 1/2 and 3/2 has been analysed theoretically. The analysis reveals that under the influence of the S= 1/2 spin state, the Kramers doublets of S=3/2 split with Sz=+or-3/2 being the ground state in contrast to the case of the S=5/2 and S=3/2 admixture. The study of the mixing of spin S= 1/2 with admixed spin 3/2-3/2 states shows that when S= 1/2 states are brought closer to the mixture, keeping the 5/2-3/2 gap at a constant value, the two Kramers doublets of S=3/2 come closer to each other, cross over and become inverted. The effect of this crossover on the magnetic susceptibility and EPR signals is also discussed.