Influence of magnetic fields on cold collisions of polar molecules

We consider cold collisions of OH molecules in the $^2\Pi_{3/2}$ grounds state, under the influnce of a magnetic field. We find that modest fields of several thousand gauss can act to suppress inelastic collisions of weak-field seeking states by two orders of magnitude. We attribute this suppression to two factors: (i) An indirect coupling of the entrance and the exit channel, in contrast to the effect of an applied electric field; and (ii) the realtive motion of the entrance and exit scattering thresholds. In view of these results, magnetic trapping of OH may prove feasible.