# THE $B^{1}\Pi_{u} - X^{1}\Sigma_{g}{^{+}}$ BAND OF THE $^{7}Li_{2}$ MOLECULE

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 Title: THE $B^{1}\Pi_{u} - X^{1}\Sigma_{g}{^{+}}$ BAND OF THE $^{7}Li_{2}$ MOLECULE Creators: Hessel, M. M.; Vidal, C. R. Issue Date: 1978 Publisher: Ohio State University Abstract: Velasco and coworkers were first to determine the ground state constants for the $B^{1} \Pi_{u} \rightarrow X^{1} \Sigma_{g}{^{+}}$ band system of $Li_{2}$ by laser excitation. We have used both laser fluorescence and absorption spectroscopy at high resolution and dispersion to obtain the spectra of this $Li_{2}$ band system. Over 14 000 spectral lines have been assigned to this band system for a wide range of quantum numbers $(J = 2 - 8O, v^{\prime} = 0 - 14, v^{\prime\prime} = 0 - 20)$. Using a Dunham analysis, we have obtained molecular constants for both states and have fitted about 9000 non-overlapping lines with an rms error of $0.012\, cm^{-1}$. The $B^{1} \Pi_{u}$ lambda doubling constants, including the centrifugal distortion lambda doublet splitting have been determined. Excellent agreement has been achieved between the centrifugal distortion terms $D_{v}, H_{v}$, and $L_{v}$ which were obtained from a least squares fit of the assigned lines and those calculated by the technique of Albritton et al. from the quantum mechanical rotationless potential. Levels above the $2^{2} P + 2^{2} S_{1/2}$ dissociation limit have been observed and a barrier height of $410 \pm 50$ $cm^{-1}$ for the $B^{1} \Pi_{u}$ state was found. The dissociation energy of the $X^{1} \Sigma_{g}$ state was found to be $862O \pm 100$ $cm^{-1}$. Quantum mechanical potential curves have been generated using a novel variational procedure and Franck-Condon factors have been determined for several different rotational quantum numbers over the range of vibrational levels observed. Description: Author Institution: Molecular Spectroscopy Division, National Bureau of Standards; Max Planck Instit\""{u}t f\""{u}r Extraterrische Physik, National Bureau of Standards URI: http://hdl.handle.net/1811/10593 Other Identifiers: 1978-TB-11