Knowledge Bank

Fluorescence in the $C2\Pi u-12\Pi g21\Sigma u\ast -12\Pi g$ and $21\Sigma u\ast -21\Sigma g\ast$ transitions of $\mathrm{<mrow\; data-mjx-texclass="ORD">7</mrow>}Li2$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}Li2$. excited by ultraviolet lines of argon and krypton ion lasers, has been studied in the region $7000-12000cm-1$ using a Fourier Transform spectrometer. The rotational analysis concentrates on $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}Li2$. In $C2\Pi u12\Pi g$ fluorescence, long progressions, up to $v=34$, are observed in the $12\Pi g$ state. The Dunham coefficients obtained from the analysis are in good agreement with ab-initio calculations. From the data, an RKR potential curve has been constructed for the $12\Pi g$ state. The dissociation energy has been calculated by several independent methods giving a 1best value1 of $1422.030.05cm-2$. The A-doubling in both isotopomers is found to be irregular, both with respect to vibration and rotation. The interaction between the $12\Pi g$ and $21\Sigma g$ states has been studied in detail and is shown to account for the observed Irregularities. The same interaction also accounts for some very strong perturbations observed in the $12\Pi g$ and $21\Sigma g$ states of $21\Sigma u$ Some of these perturbations show very clear intensity interference effects. From an examination of intensity anomalies, ratios of transition moments of $21\Sigma u-12\Pi g$ and $21\Sigma u-21\Sigma g$ transitions have been determined. Details of the above studies will be presented and the results discussed and compared with ab-inltio predictions.