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Nesbet in 1964$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$, calculated that $Mn2$ should be an antiferromagnetic molecule ($\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma g+$ lowest State) with an exchange interaction constant J =-$4.1cm-1$ It is here reported that this has been verified by electron-spin-resonance spectroscopy of the $Mn2$ molecule formed in solid krypton and xenon matrices at $4\circ K$ by measurements at higher temperatures. The complexity of the spectra increase as the temperature rises, with each line split Into II distinct hyperfine components separated by 15 G and with relative intensities 1:2:3:4:5:6:5:4:3:2:1. This splitting is about one-half for that for single $\mathrm{<mrow\; data-mjx-texclass="ORD">55</mrow>}$Mn atoms as expected for two exchange-coupled atoms. Tentative assignments indicate that $J=-20cm-1$ and that the zero-field-splitting in the S = 2 and S = 3 spin states are $|D|\simeq$ 0.14 and $0.07cm-1$, respectively. Other research, suggested by these observations, will be mentioned. $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$R.K. Nesbet, Phys, Rev. A135, 460 (1964).