  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 Hund's case (c) 2 (0g+) state, which
correlates to the Hund's 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.
