  A mean field theory of expanding hybrid atom-molecule Bose-Einstein
condensates is applied to the recent MPI experiments on ${}^{87}$Rb that
demonstrated the formation of ultracold molecules due to Feshbach resonance.
The subsequent dissociation of the molecules is treated using a non-mean-field
parametric approximation. The latter method is also used in determining optimal
conditions for the formation of molecular BEC
