Isomers and Isomags in MnnX (n = 5-6, X=N, O) Clusters

It is shown that the addition of N or O to pure Mn$_{n}$ clusters can lead to situations where the ground state is marked by configurations having comparable binding energies, same total spins but differing distribution of local moments. We call these ``isomags'' and demonstrate their existence through a synergistic approach combining negative ion photo-detachment spectra and theoretical investigations. In the case of Mn$_{5}$O and Mn$_{6}$O clusters show that the O atom occupies either bridge or hollow sites. While it occupies a bridge site with a binding energy of 6.88 eV in Mn$_{5}$, it prefers a hollow site with a binding energy of 7.18 eV in Mn$_{6}$ clusters. Further, Mn$_{5}$O is shown to possess two magnetic isomers with total spins of 13 and 5 $\mu _{B}$ that contain three and five isomags respectively. Mn$_{6}$O possesses three isomers, two with moments of 8 and 2 $\mu _{B}$ in addition to a non-magnetic state. It is shown that the isomags, although undetected in magnetic deflection experiments, can be traced via their electronic structure in experimental photoelectron spectra. Corresponding results on Mn$_{n}$N will also be presented.