S-mixing and quantum tunneling of the magnetization in molecular   nanomagnets
  The role of $S$-mixing in the quantum tunneling of the magnetization in nanomagnets has been investigated. We show that the effect on the tunneling frequency is huge and that the discrepancy (more than 3 orders of magnitude in the tunneling frequency) between spectroscopic and relaxation measurements in Fe$_8$ can be resolved if $S$-mixing is taken into account. 
S. Carretta, E. Liviotti, N. Magnani, P. Santini and G. Amoretti