The Beryllium Molecule

The interaction of a normal Be atom with one which has an electronic configuration $2s2p$ has been studied by means of the Heitler-London method. Of the eight possible molecular states, two are calculated to be stable, namely ${}_{}{}^1{}_{}{}^{}\Sigma A^N$ and ${}_{}{}^1{}_{}{}^{}\Pi A^N$, and the ${}_{}{}^1{}_{}{}^{}\Sigma$ state is the lower of the two. An attempt to obtain agreement with experiment in the case where a normal Li atom interacts with one in the $2p{}_{}{}^2{}_{}{}^{}P$ state has not been successful, at least for the resulting $\Pi$ states.