Dynamical instability and external perturbations: Bimolecular collisions in laser fields

The detailed dynamics of F+H2, and to a lesser extent H+H2, in the presence of laser fields are examined in order to establish the relationship between field-free unstable trajectories and the effect of external perturbations. Weak fields are found to alter the dynamics of individual unstable trajectories and, in particular, to induce transitions amongst the unstable trajectory manifold. As a result, the field has little effect, on the average, on gross collision properties. Intense fields substantially alter the qualitative stable/ unstable structure of phase space and hence the reaction probability. An interesting high field limit is also discussed.