LIF STUDIES OF GROUP IIA DIMERS PRODUCED BY LASER VAPORIZATION OF THE METALS

Two electronic transitions of $Be_{2}$ are observed and $analyzed^{1}$. The $X^{1} \\Sigma_{g}^{+}$ ground state is characterized by a relatively shallow potential well with $D_{e} \\sim 900 cm^{-1}, re=465$ {\\AA}, and $\\Delta G_{1/2}=223.4 cm^{-1}$.. The excited electronic states, $A^{1} \\Pi_{u} (\\nu_{00}=21678.4 cm^{-1}, re=1. 995${\\AA}, $\\omega=686 cm^{-1}, W_{e} X_{e} \\sim 4.5 cm^{-1}$), and $B^{1} \\Sigma_{u}^{+} + (V_{00} =27857.8 cm^{-1}, r_{e}=2. 16A, \\omega=504 cm^{-1}$, the lowest $^{1}\\Pi_{g}$ state will be also discussed. Similar studies involving the $Mg_{2}$ and $Ca_{2}$ diatonics will be described. It is proposed that a spectrum observed previously near $22000 cm^{-1}$ in matrix isolated $Mg_{2}$ and assigned as the forbidden $X^{1} \\Sigma_{g}^{+} \\to ^{1}\\Pi_{g}$ transition is, in fact, due to the $A^{1}\\Pi_{u}$ state, analogous to the corresponding state of $Be_{2}$. Analysis of $Ca_{2}$ spectrum confirms unambiguously the existence of a low lying $A^{1}\\Sigma_{u}$ state in the red with $w_{e} \\sim 120 cm^{-1}$, as originally suggested by matrix $experiments^{3,4}$ and theoretical $calculations^{5}$.