Heavy atom tunneling in chemical reactions: study of H + LiF collisions.

The H+LiF(X (1)sigma(+),upsilon=0-2,j=0)-->HF(X (1)sigma(+),upsilon',j')+Li(2S) bimolecular process is investigated by means of quantum scattering calculations on the chemically accurate X 2A' LiHF potential energy surface of Aguado et al. [A. Aguado, M. Paniagua, C. Sanz, and J. Roncero, J. Chem. Phys. 119, 10088 (2003)]. Calculations have been performed for zero total angular momentum for translational energies from 10(-7) to 10(-1) eV. Initial-state selected reaction probabilities and cross sections are characterized by resonances originating from the decay of metastable states of the H...F-Li and Li...F-H van der Waals complexes. Extensive assignment of the resonances has been carried out by performing quasibound states calculations in the entrance and exit channel wells. Chemical reactivity is found to be significantly enhanced by vibrational excitation at low temperatures, although reactivity appears much less favorable than nonreactive processes due to the inefficient tunneling of the relatively heavy fluorine atom strongly bound in van der Waals complexes.