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This work reports a series of absorption and magnetic circular dichroism (MCD) studies of manganese atoms and higher aggregates matrix-isolated in Ar and Xe matrices. MCD signals corresponding to the two known atomic $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}P\leftarrow 6S$ transitions were intense, showed a strong temperature dependence, and exhibited a triplet of bands with separation much larger than the spin-orbit splittings of the $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}P$ states. An excited state Jahn-Teller interaction is indicated and is being further studied by an analysis of band moments. Absorption bands at 346.5 nm and nm 331.5 nm (Mn/Ar) which increase in intensity with temperature have been attributed to the antiferromagnetic $Mn2$ molecule. Finally, irradiation of an unknown molecular band at -400 nm in argon and xenon matrices appears to produce an optically-active species. Tentative assignment to a packered $Mn5$ ring molecule is proposed. Work is continuing on other atomic and cluster transitions.