Excited-state X-band EPR in a molecular cluster nanomagnet

The X-band excited-state electron paramagnetic resonance (EPR) spectra of ${\mathrm{Mn}}_{12}$-acetate nanomagnet crystals has been measured. Three lines belonging to the $m=\ensuremath{-}1\ensuremath{\leftrightarrow}0$ transition at ${H}_{C}=600\mathrm{G}$ and to the $m=0\ensuremath{\leftrightarrow}\ensuremath{-}1$ and $m=\ensuremath{-}2\ensuremath{\leftrightarrow}\ensuremath{-}1$ high-field transitions at 7800 and 9200 G, respectively, were detected below 50 K in agreement with the energy level scheme obtained from high-field EPR. The lines are rather broad. ${T}_{2}$ is shorter than 30 ns and ${T}_{1}{T}_{2}l{10}^{\ensuremath{-}15}{\mathrm{s}}^{2}.$ Similarly broad excited-state EPR spectra were also observed in a Fe(8) single crystal.