Magnetic field effects on the far-infrared absorption in Mn-12-acetate - art. no. 214408

We report the far-infrared spectra of the molecular nanomagnet Mn-12-acetat e (Mn-12) as a function of temperature (5-300 K) and magnetic field (0-17 T ). The large number of observed vibrational modes is related to the low sym metry of the molecule, and they are grouped together in clusters. Analysis of the mode character based on molecular-dynamics simulations and model com pound studies shows that all vibrations are complex; motion from a majority of atoms in the molecule contribute to most modes. Three features involvin g intramolecular vibrations of the Mn-12 molecule centered at 284, 306, and 409 cm(-1) show changes with applied magnetic field. The structure near 28 4 cm(-1) displays the largest deviation with field and is mainly intensity related. A comparison between the temperature-dependent absorption-differen ce spectra, the gradual low-temperature cluster framework distortion as ass essed by neutron-diffraction data, and field-dependent absorption-differenc e spectra suggests that this mode may involve Mn motion in the crown.