AN OVERVIEW OF THE STRUCTURE AND SPECTRA OF THE 26 LOWEST-LYING STATES OF $Li_{2}$

Ab initio configuration-interaction computations which invoke an effective core potential approximation are used to describe the 26 lowest-lying states of $Li_{2}$. The quality of the computations are assessed by an analysis of the asymptotic long-range behavior of the potentials and by a comparison of the computed vibrational energy levels with those deduced from spectra. Typical asymptotic results are: $C_{6} = 1430 (1400) e^{2}{a_{0}}^{5}$ for the $1 ^{1}{\Sigma^{+}}_{g}$ and $1^{3}{\Sigma^{+}}_{u}$ states: $C_{3} = 11.14 (11.04) e^{2}{a_{0}}^{2}$ for the $2^{1}{\Sigma^{+}}_{g}$ and $2^{3}{\Sigma^{+}}_{u}$ states. (Literature values are in parenthesis). Scaling the calculated $1^{1}{\Sigma^{+}}_{g}$ potential curve against observed vibrational energy spacings gives a dissociation energy $D_{e} = 8490 (8450,8505) cm^{-1}$. We make special mention of ion-pair effects on the structure and spectra of a number of states