Observation and Analysis of Resonant Coupling Between Near-Degenerate Levels of the 2 1Sigma g+ and 1 1 Pi g States of Ultracold 85Rb2

We report on the anomalously high line strength of a single rotational level in the ultracold photoassociation of two 85Rb atoms to form 85Rb2. The v = 111, J = 5 level belongs to the Hunds case (c) 2 (0g+) state, which correlates to the Hunds case (a) 2 1 Sigma g+ state. Its strength is caused by coupling with a very near-resonant long-range state. The long-range component is the energetically degenerate v = 155, J = 5 level of the case (c) 2 (1g)$ state, correlating to the case (a) 1 1 Pi g state. The line strength is enhanced by an order of magnitude through this coupling, relative to nearby vibrational levels and even to nearby rotational levels of the same vibrational level. This enhancement is in addition to the enhancement seen in all J = 3 and 5 levels of the 2 (0g+) state due to an l = 4 shape resonance in the a 3 Sigma u+ state continuum, which alters the distribution of levels formed by photoassociation.

Photoassociation to the 2(1)Sigma(g)(+) state in ultracold 85Rb2 in the presence of a shape resonance

We report the first observation of photoassociation to the 2(1)Sigma(g)(+) state of 85Rb2 . We have observed two vibrational levels (v=98, 99) below the 5s1/2+5p1/2 atomic limit and eleven vibrational levels (v=102-112) above it. The photoassociation---and subsequent spontaneous emission---occur predominantly between 15 and 20 Bohr in a region of internuclear distance best described as a transition between Hunds case (a) and Hunds case (c) coupling. The presence of a g-wave shape resonance in the collision of two ground-state atoms affects the photoassociation rate and lineshape of the J= 3 and 5 rotational levels.

Formation of ultracold metastable Rb2 molecules in their v=0 level by blue-detuned photoassociation

We report on the observation of blue-detuned photoassociation in Rb2, in which vibrational levels are energetically above the corresponding excited atomic asymptote. 85Rb atoms in a MOT were photoassociated at short internuclear distances to levels of the (1)3Pi g state at a rate of approximately 5x10^4 molecules/s. We have observed most of the predicted vibrational levels for all four spin-orbit components 0g+, 0g-, 1g, and 2g, including levels of the 0g+ outer well. These molecules decay to the metastable a3Sigma u+ state, some preferentially to the v=0 level, as we have observed for photoassociation to the v=8 level of the 1g component.