Quantum Dynamics Method Studies On The Energy Efficiency In Surmounting The Barrier Of The Polyatomic Reactions

A time-dependent, reduced-dimensional quantum reaction dynamics method was carriedout to study the energy efficiency in surmounting the reaction energy barrier of OH+CH3, F+CHD3/CD4and HCl+CH3/CD3in this paper.The current6/7free-of-degree quantum dynamics study of the OH+CH3reaction with a"central"(slightly early) barrier shows, the reactant OH vibrational energy is more effective inenhancing the reaction than the translational energy; whereas for its forward reaction O+CH4also with a "central"(slightly late) barrier, the previous studies display that, the translationalenergy is more effective in surmounting the barrier than the vibrational energy. Thevibrational excitations of reactant CH3have the inhibitory effect. Since both barriers onlyslightly deviate from the center of the potential energy surface, these findings indicate that forthe reaction with more-or-less central barriers, a small change of the barrier location cangreatly affect which energy form determines the reaction reactivity. This study also showsboth the rotational excitation states of OH and CH3hinder the reactivity.We presented a four-free-of-degrees model calculations for the early barrier reaction F+CHD3/CD4. A resonance is found in the reaction probabilities, which is in agreement with theexperimental prediction. Both the excited vibrations of the CH/CD stretching mode and theCD3in CD4umbrella motion promote the reactivity, while the umbrella mode excitations ofCD3in CHD3restrain the reaction in barrier-crossing. Additionally, except at the highertranslational energy the Polanyi rules can be applied to this early barrier reaction.We employed the same6free-of-degree reduced dimensional model to study the reversereaction HCl+CH3/CD3of the Cl+CH4/CHD3reaction. Similarly, the calculations show that,the reactant HCl vibration excitations play a efficient role on surmounting the energy barrier;but the vibrational excitations of CH3/CD3and the rotational excitations have the oppositeeffect.Based on quantum dynamics calculational results of the three polyatomic reactions, weconclude, the well-known Polanyi rules can not be directly applied to predict the energy efficiency of the polyatomic reactions. More experimental and theoretical studies need to bedone to generalize the energy efficacy roles in overcoming the barrier reactions.