Submillimeter spectroscopy of Mn-12-Ac magnetic clusters

Transitions inside the ground S = 10 multiplet of magnetic clusters Mn-12-A c have been observed in submillimeter transmission spectra measured by mean s of a quasi-optical backward-wave-oscillator technique in the frequency ra nge nu = 3-33 cm(-1). The temperature dependence of the resonance frequenci es, linewidths and mode contributions to the magnetic permeability in the r ange T = 3-35 K are consistent on the whole with a spin S = 10 ground state split by a tetragonal crystal field. However, some deviations between the calculated and observed mode contributions at high temperatures suggest the presence of other Mn-12-Ac excited multiplets with S not equal 10.