Quantum dynamics calculations reveal temperature independence of kinetic isotope effect of the OH + HBr/DBr reaction

Time-dependent quantum dynamics study of the F + C2H6 → HF + C2H5 reaction

The reaction probabilities, integral cross sections, energy efficiency and rate constants are investigated for the F + C₂H₆ reaction using the quantum reaction dynamics, wave packet method. The ground-state integral cross section calculated using a six-degree-of-freedom approach is in very good agreement with the quasi-classical trajectory results. We find that the H-CH₂CH₃ stretching motion has the largest enhancement to reactivity, followed by the H-CH₂-CH₃ bending motion. However, the stretching motion between CH₂ and CH₃ slightly hinders the reactivity. The energy-form efficacy based on an equal amount of total energy shows that translational energy is more effective in enhancing the reactivity than vibrational energy of the H-CH₂CH₃ stretching motion at a relatively lower translational energy, while the reverse is true at a relatively high translational energy. An energy-shifting method is employed to calculate the full-dimensional rate constants. The quantum rate constants agree well with one of the two main experimental measurements, and the activation energy has an excellent agreement with the one calculated using canonical variational transition-state theory.

Using quantum dynamics to study the effect of energy efficiency on the reactivity of the OH + DBr reaction

We report a time-dependent, full dimensional, wave-packet calculation for the reaction of OH + DBr to examine the effect of the energy efficiency on the reactivity. This study shows that the vibrational excitations of the OH and DBr enhance the reaction. However, the rotational excitations of OH and DBr both hinder the reaction. As a result, the vibrational energies of both the OH and DBr reactants are more efficient at promoting the reactivity than the translational energy, while the rotational energies of OH and DBr are less effective than the translational energy. By analyzing the state population of the vibrational and rotational states along the reaction pathway, we also developed an approach in order to explain the enhancement of the vibrational excitation and the hindrance of the rotational excitation of the reaction. We found that the initial-state selected vibrational excited states of OH and DBr are the dominant components, respectively, for surmounting the barrier. However, the initial-state selected rotational excited states of OH and DBr are no longer the dominant states for surmounting the transition state owing to their population changes in the van der Waals well. This quantitative analysis demonstrates the potential well in the entrance valley plays an important role in the energy efficiency with regards to the reactivity.

Quantum dynamics study of kinetic isotope effects of OD with HBr and DBr

Comparison of kinetic isotope effects between quantum dynamics calculations and experiments shows that they agree well with each other both qualitatively and quantitatively.