  We have studied the effects of loading $^{87}$Rb into a far off resonant trap
(FORT) in the presence of an ultracold cloud of $^{85}$Rb. The presence of the
$^{85}$Rb resulted in a marked decrease of the $^{87}$Rb load rate. This
decrease is consistent with a decrease in the laser cooling efficiency needed
for effective loading. While many dynamics which disrupt loading efficency
arise when cooling in a dense cloud of atoms (reabsorption, adverse optical
pumping, etc.), the large detuning between the transitions of $^{85}$Rb and
$^{87}$Rb should isolate the isotopes from these effects. For our optical
molasses conditions we calculate that our cooling efficiencies require induced
ground-state coherences. We present data and estimates which are consistent
with heteronuclear long-ranged induced dipole-dipole collisions disrupting
these ground state coherences, leading to a loss of optical trap loading
efficiency.
