Quantum dynamics study of C-H stretching vibrational excitation in the F+CHD<sub>3</sub> → HF+CD<sub>3</sub> reaction

In recent decades, significant progress has been made in the precise theoretical investigation of gas-phase chemical reactions. Presently, a major challenge in the field of quantum dynamics is the development of precise methodologies for studying chemical reactions involving more than four atoms. As a typical multi-atomic reaction system, the F+CH₄ reaction and its isotopic substitution reactions have attracted widespread attention from both experimental and theoretical perspectives in recent years. Experimental studies on the reaction of F+CHD₃ revealed that the stretching vibration excitation of the C-H bond inhibits the bond dissociation, favoring the formation of DF+CHD₂ products channel. In this study, we employed a seven-dimensional quantum time-dependent wave packet method to investigate the dynamics of the F+CHD₃ reaction in both the reactant vibrational ground state and the first stretching excited state of the C-H bond. The paper analyzed reaction probabilities under different vibrational conditions, revealing that when the collision energy is below 0.06 eV, the reaction probability curves exhibit numerous fast-oscillating peaks, supporting the experimentally suggested phenomena of dynamic resonance. At collision energies ranging from 0.06 eV to 0.3 eV, the reaction probability for the HF product channel in the vibrational excited state was lower than that in the ground state, consistent with experimental observations. Through the analysis of the time-independent wave functions of product channels under low-energy collision conditions, we have found that for reactions involving vibrational ground states, the HF products in the product asymptotic region and the reaction transition state region are in the v'=2 and v'=3 excited states of stretching vibration, respectively, consistent with previous experimental observations and six-dimensional quantum wave packet simulations. For reactions involving the first excited state of C-H stretching vibration, the HF products in the product asymptotic region and the reaction transition state region are both in the v'=3 excited state of stretching vibration, consistent with the results obtained based on energy analysis. Simulation results indicated that, in the case of low-energy collisions, the time-independent wave function for the C-H stretching vibrational excited state tends to be closer to the D atom side in the transition state region. This phenomenon was attributed to the more significant energy advantage of the vibrational excited state potential energy surface in the large collision angle region, explaining the inhibitory effect of stretching vibration excitation on the HF product channel. This study offers crucial theoretical support for interpreting experimental results and contributes to a deeper understanding of the influence of vibrational mode excitations on the dynamical processes in poly-atomic reactions.