Monte Carlo calculations of reaction rates and energy distributions among reaction products. IV. F+HF(ν) → HF(ν′)+F and F+DF(ν) → DF(ν′)+F

Abstract

Rate constants are calculated for the vibrational relaxation HF(ν) and DF(ν) molecules by F atoms with ν = 1, 2, 3, and 6. Three-dimensional classical trajectories of the collision dynamics of these reactions were calculated by means of a modified London-Eyring-Polanyi-Sato (LEPS) potential energy surface used to calculate rate constants for the reactions between H atoms and F2 molecules, and D atoms and F2 molecules. The Monte Carlo procedure is used to start each collision trajectory. By means of this calculation, it is predicted for the reactant HF molecule in the ν = 2, J = 8 state that 13.3% of the mean fraction of available energy will become rotation in the product HF, 80.7% will become vibrational energy in the product HF, and 6% will become relative translational energy of the products. As the vibrational energy of the reactant HF molecule increases the mean fraction of available energy that becomes rotational energy increases slightly. For example, if the reactant molecule HF is in the ν = 6, J = 8 state, it is found that the mean fraction of available energy that will become rotational energy in HF is 15.8%, 75.3% will become vibrational energy in HF, and 8.9% will become translational energy in the product. Two different methods are used to calculate the rate constants kν→ν−1 for the de-excitation of vibrationally excited HF molecules by F atoms. The main mechanism for the de-excitation of vibrationally excited HF or DF molecules by F atoms is vibration-rotation energy transfer. Multiple quantum transitions occur in the de-excitation of higher (ν ≥slant 3) vibrationally excited states of HF molecules by F atoms. Chemical effects provide an important mechanism for the efficient vibrational relaxation of HF and DF molecules by F atoms. Rate constants are provided for many reactions that have not been measured experimentally.