The absorption and laser induced fluorescence spectra of theB1Pgr;undash;X1Sgr;g+band system of the7Li2molecule has been photographed at high resolution (360thinsp;000) and high dispersion (0.4 Aring;/mm). Over 14thinsp;000 spectral lines have been assigned to this band system for a wide range of rotational quantum numbers (J=0minus;80) and vibrational quantum numbers (vprime;=0minus;13 andvPrime;=0minus;18). Using a Dunham type analysis, we have obtained the molecular constants for both states and have fitted 8358 nonoverlapping lines with an rms error of 0.012 cmminus;1. TheB1Pgr;ulambda doubling constants, including the centrifugal distortion lambda doublet constant, have been determined. Quantum mechanical potential curves have been generated for this system using a novel variational procedure and Franckndash;Condon factors for different rotational quantum numbers have been determined over the range of vibrational levels observed. Excellent agreement has been achieved for the centrifugal distortion termsDv,Hv, andLVwhich were obtained from the least squares fit of the assigned lines and those calculated from the quantum mechanical rotationless potential. Levels above the 22P+22S1/2dissociation limit have been observed and a maximum for the barrier in theBthinsp;1Pgr;upotential of 450plusmn;50 cmminus;1above this atomic level was found. The dissociation energy,Deprime; of theXthinsp;1Sgr;gstate was found to be 8600plusmn;150 cmminus;1. A review of the literature on the Li2molecule through 1977 is given.
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