Excitation and fluorescence spectra of the Cs2molecule were measured with high resolution allowing resolution of the rotational structure. These spectra were studied under excitation by different lines of a single mode argon laser which could be continuously tuned across spectral intervals of about 10 GHz. For excitation in a cesium vapor cell the spectral resolution was only limited by the Doppler width of the absorption lines while in a collimated cesium beam a resolution between 20 and 60 MHz could be achieved. Accurate molecular constants and the RKR potential of theXthinsp;1Sgr;+gground state are derived from more than 900 fluorescence lines, most of which were precisely measured with a Fabryndash;Perot interferometer crossed with a monochromator. The dissociation energy of the ground state is deduced from an extrapolation beyond the highest measured level withvPrime;=72, and also from a second laserhyphen;excited fluorescence spectrum that appears at the red end of the singlet spectrum and consists of a continuum and a few discrete lines. This spectrum is assigned to transitions terminating in theXthinsp;3Sgr;+ustate, which is mainly repulsive. Like theXthinsp;1Sgr;+gstate, it too dissociates into two Cs atoms in their 6thinsp;2S1/2ground states.
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