Knowledge Bank

Two electronic transitions of $Be2$ are observed and $analyzed1$. The $X1\Sigma g+$ ground state is characterized by a relatively shallow potential well with $De\sim 900cm-1,re=465$ {\AA}, and $\Delta G1/2=223.4cm-1$.. The excited electronic states, $A1\Pi u(\nu 00=21678.4cm-1,re=1.995${\AA}, $\omega =686cm-1,WeXe\sim 4.5cm-1$), and $B1\Sigma u++(V00=27857.8cm-1,re=2.16A,\omega =504cm-1$, the lowest $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi g$ state will be also discussed. Similar studies involving the $Mg2$ and $Ca2$ diatonics will be described. It is proposed that a spectrum observed previously near $22000cm-1$ in matrix isolated $Mg2$ and assigned as the forbidden $X1\Sigma g+\to 1\Pi g$ transition is, in fact, due to the $A1\Pi u$ state, analogous to the corresponding state of $Be2$. Analysis of $Ca2$ spectrum confirms unambiguously the existence of a low lying $A1\Sigma u$ state in the red with $we\sim 120cm-1$, as originally suggested by matrix $experiments3,4$ and theoretical $calculations5$.