Monte Carlo calculations of reaction rates and energy distribution among reaction products. II. H+HF(v) → H2 (v′) + F and H+HF(v) → HF(v′) + H

Abstract

Rate constants are calculated for the reactions of atomic hydrogen with vibrationally excited hydrogen fluoride by analyzing the results of classical trajectories on a semiempirical London-Eyring-Polanyi-Sato (LEPS) potential energy surface. Monte Carlo procedures are used to start each collision trajectory. Reaction rate constants are presented for direct reactions into specific vibrational states of the product H2 and HF molecules. By means of this calculation, it is predicted for the reactant HF molecule in the ν = 3 state that 11.3% of the mean fraction of available energy will become vibrational energy in H2, 1.2% will become rotational energy in H2, and 87.5% will become translational energy in the products. As the vibrational energy of the reactant HF molecule increases, the mean fraction of available energy which becomes vibrational energy of the product H2 molecule increases. For example, if the reactant molecule HF is in the v = 6 state, it is found that the mean fraction of available energy that will become vibrational energy in H2 is 35.1%, 8% will become rotational in H2, and 56.9% will become translational energy in the products. For the reactant HF molecule in the v = 3 state, 45% of the mean fraction of available energy will become vibrational energy in the product HF molecule, 0.4% will become rotational energy in HF, and 54.8% will become translational energy in the products. The de-excitation of HF by H atoms is due to vibration-translation energy transfer. Results of this trajectory calculation, indicate that (1) multiple quantum jumps are significant in the reactions of H atoms with vibrationally excited HF, and (2) chemical effects provide an important mechanism for the efficient relaxation of vibrationally excited HF by H atoms. Both theory and experiment indicate that the rate of deactivation of vibrationally excited HF by H atoms is very fast. Rate constants are provided for many reactions that have not been measured experimentally.