  We study theoretically several aspects of the dynamics of coherent
atom-molecule conversion in spin-1 Bose-Einstein condensates. Specifically, we
discuss how for a suitable dark-state condition the interplay of spin-exchange
collisions and photoassociation leads to the stable creation of an atom-
molecule pairs from three initial spin-zero atoms. This process involves two
two-body interactions and can be intuitively viewed as an effective three-body
recombination. We investigate the relative roles of photoassociation and of the
initial magnetization in the \resonant" case where the dark state condition is
perfectly satisfied. We also consider the "non-resonant" regime, where that
condition is satisfied either approximately {the so-called adiabatic case {or
not at all. In the adiabatic case, we derive an effective non-rigid pendulum
model that allows one to conveniently discuss the onset of an antiferromagnetic
instability of an \atom-molecule pendulum," as well as large-amplitude pair
oscillations and atom-molecule entanglement.

Quantum Gases;Atomic Physics;Quantum Physics