A theoretical study of the prereaction process of the H center dot center dot center dot HF van der Waals molecule

Three-dimensional time-independent reactive scattering calculations have be en carried out to simulate the dissociation process of the H ... HF van der Waals (vdW) molecule by infrared excitation. The most recent ab initio pot ential energy surface of Stark and Werner has been employed to obtain the s cattering wavefunctions, while the bound-state wavefunction for the H ... H F vdW complex has been modeled with a simple harmonic oscillator. We have f ound the prereaction process, H ... HF* --> H-2 + F, occurs in the tunnelin g region and also on the vdW resonance positions, where H ... HF* correspon ds to the quasi-bound vdW resonance state in which HF is vibrationally (or rotationally) excited, although the predissociation process, H ... HF* --> H-2 + F, dominates in the energy range considered in the present calculatio ns. This result indicates that both the prereaction and predissociation pro cesses take place in the similar time scale at least on the Stark-Werner po tential surface.