We have formed ultracold Rb{sub}2 molecules in a dark MOT using one-color photoassociation of laser-cooled 87{sup left}Rb atoms. The number of 87{sup left}Rb atoms in the dark MOT is about 5 × 10{sup}9 and the density is about 5 × 10{sup}11 cm{sup}-3. The photoassociation laser drives transitions between the free states of colliding pairs of atoms and the v = 1 vibrational level of the Rb{sub}2 0{sub}g{sup}-"pure long range state". Spontaneous emission of these electronically excited molecules yields Rb{sub}2 molecules in high lying vibrational levels of the ground triplet state. This process has a favorable Franck-Condon factor because the vibrational energy of the 0{sub}g{sup}-(v = 1) level is so small. We detected these molecules using resonance-enhanced multiphoton ionization induced by a pulsed dye laser tuned near 805 nm, followed by detection of the resulting ions with a channeltron.
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