Photoassociative Spectroscopy and Formation of Cold Molecules in Cold Cesium Vapor: Trap-Loss Spectrum versus Ion...

We report on the experimental spectra of all the optically accessible long-range attractive molecular states of the Cs2 dimer below the 6s2S1/2 + 6p2P3/2 dissociation limit by molecular photoassociation of cold Cs atoms. The spectra are obtained by the usual trap-loss method as well as by pulsed-laser photoionization of Cs2 molecules into Cs+2 ions. The two spectra present markedly different features. While the 1g, 0(+)u, and 0(-)g vibrational progressions are present in the trap-loss spectrum, the Cs+2 ion spectrum presents only the 0(-)g and 1u vibrational progressions. Those states (0(-)g and 1u) lead to the formation of the translationally cold Cs2 ground state molecules at temperatures in the 100 µK range, to our knowledge the lowest molecular temperature reported up until now. The C3 asymptotic coefficients for the 0(+)u and 1g states are determined through a fit of the experimental energy levels. Copyright 1999 Academic Press.