Linewidth of single-photon transitions in Mn-12-acetate - art. no. 184426

We use time-domain terahertz spectroscopy to measure the position and linew idth of single-photon transitions in Mn-12-acetate. This linewidth is compa red to the linewidth measured in tunneling experiments. We conclude that lo cal magnetic fields (due to dipole or hyperfine interactions) cannot be res ponsible for the observed linewidth and suggest that the linewidth is due t o variations in the anisotropy constants for different clusters. We also ca lculate a lower limit on the dipole field distribution that would be expect ed due to random orientations of clusters and find that collective effects must narrow this distribution in tunneling measurements.