Experimental Determination of the Rotational Constants of High-Lying Vibrational Levels of Ultracold Cs₂ in the 0_g^– Purely Long-Range State

We report on a quantitative experimental determination of the rotational constants for the high-lying vibrational levels of the ultracold pure long-range Cesium molecules formed via photoassociation. The scheme relies on a precise reference of frequency difference in a double photoassociation spectroscopy, which is induced by two laser beams based on an acoustic-optical modulator. The rotational constants are obtained by fitting a nonrigid rotor model into the frequency intervals of the neighboring rotational levels deduced from the reference

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2D spectra as a function of waiting tim