THE LOW-LYING ELECTRONIC STATES OF $Zn_{2}$.

Abstract

Promising systems as visible and near ultraviolet lasers include the Group IIB dimers, $Zn_{2}, Cd_{2}$, and $Hg_{2}$, with dissociative ground states but low-lying bound excited states. To provide a better theoretical understanding of this series of molecules, we report ab initio configuration interaction calculations on the states of $Zn_{2}$ which dissociate to $Zn(^{1}S) + Zn(^{1}S, ~^{3}P, ^{1}P)$. As expected from simple theoretical considerations, the ground state and two of the triplet states $(^{3}\Sigma_{g}^{+}, ^{3}\Pi_{u})$ are essentially repulsive with only shallow van der Waals minima. The other two triplet states $(^{3}\Sigma_{u}^{+}, ^{3}\Pi_{g})$ and all four excited singlet states are bound. The unexpected minima in the excited $(^{1}\Pi_{u}, ^{1}\Sigma_{g}^{+})$ states arise from interaction with states which have appreciable $Zn^{+}Zn^{-}$ ionic character. These results lead to a new interpretation of the 3350 {\AA} and 4850 {\AA} emission bands in $Hg_{2}$.