Quantum tunneling in molecular ferric wheels

An effective spin Hamiltonian is presented which describes the low-lying energy spectrum of antiferromagnetic molecular rings with high accuracy. It will be shown that for the particular case of the ferric wheels, quantum coherent phenomena are best discussed in terms of resonant quantum tunneling of the spin vector between different rotational modes. These quantum processes are associated to anticrossings of higher-lying spin multiplets with DeltaS = 2.