Narrow Subthreshold Quantum Mechanical Resonances in the Li + HF → H + LiF Reaction

State-to-state, state-specific, and cumulative reaction probabilities are presented for the bimolecular scattering process Li + HF → H + LiF in the ground electronic state. Calculations were performed for zero total angular momentum at total energies from 0.26 to 0.50 eV (relative to HF at its classical equilibrium bond distance and infinitely far from Li). The energy dependence of the state-to-state, initial-state-selected, and cumulative reaction probabilities for LiFH in the low-energy regime displays a pronounced resonance structure due to quasibound states associated with a Li···FH van der Waals well in the entrance valley of the potential energy surface. The lifetimes of the long-lived resonances are obtained by fitting the calculated eigenphase sum to the multichannel Breit−Wigner formula. The final rotational state distributions of the LiF product fragment resulting from decay of the resonance state complexes are presented for two resonances. Quantum numbers are assigned to the resonances using bound-state and quasibound-state calculations in the Li···FH van der Waals well, and possible decay mechanisms are discussed. The lifetimes show a systematic dependence on the translational vibrational quantum number.