Photoassociative spectroscopy of the Cs-2 O-g(-) long-range state

The photoassociative spectroscopy of the Cs-2 0(g)(-) long-range molecular state dissociating into the 6s S-2(1/2) + 6p P-2(3/2) asymptote is performe d, using cold cesium atoms in a vapor-cell magneto-optical trap (MOT). Vibr ational levels from v= 0 to v = 132 are identified, and their rotational st ructure is well resolved up J = 8 for levels below v = 74. These data are a nalyzed in terms of the Rydberg-Klein-Rees (RKR) procedure, and correspond to 99.6% of an effective potential curve with a minimum at 12.36+/-0.05 Ang strom and a 77.94 +/- 0.01 cm(-1) depth. Both ab initio calculations and si mple model estimations predict a double-well structure for this potential c urve, which cannot be reproduced presently by the RKR approach but which is confirmed by the presence of giant structures in the spectrum. The 1(u)(6s S-2(1/2) + 6p P-2(3/2)) long-range state is also observed for the first ti me in Cs-2.