Time delay as a tool to identify the signatures of reactive resonance:: F+HD and F+H2 reactions

The formalism of scattering time delay is investigated as a tool to identify the signatures of resonance in reactive molecular collisions. The concept of state and angle resolved time delay is reviewed and applied to model problems. Several numerical pathologies of the time delay formalism are discussed that potentially may obscure a resonance signature, or may lead to a false positive result. The time delay is computed explicitly for the F+HD-->HF+D and F+H-2-->HF+H reactions using the results of full scattering calculations on the Stark-Werner potential energy surface. The reactive resonance known to exist for the F+HD reaction is clearly apparent both in the state resolved and angle resolved time delay functions. On the other hand, the analogous resonance in the F+H-2 reaction is masked in the state resolved time delay function through the influence of a nearby energetic threshold. However, the angle resolved time delay does provide a clear signature of the resonance, thus settling a controversy on the existence of a resonance for the F+H-2 system. (C) 2003 American Institute of Physics.