Kim Junggil, Kang Minseok, Yoon Jun-Ho, Kim Sang Kyu
Department of Chemistry, KAIST, Daejeon, Republic of Korea.
Nat Commun. 2025 Jan 3;16(1):210. doi: 10.1038/s41467-024-55249-z.
Despite its profound significance, the molecular structural changes near the transition state, driven by the vibronic coupling, have remained largely unexplored, leaving a crucial aspect of chemical reactions shrouded in uncertainty. Herein, the dynamical behavior of the reactive flux on the verge of chemical bond breakage was revealed through the spectroscopic characterization of a large amplitude vibrational motion. Highly excited internal rotor states of S methylamine (CHND) report on the structural change as the molecule approaches the transition state, indicating that the quasi-free internal rotation is strongly coupled to the reaction coordinate as their energies near the maximum of the reaction barrier for the N-D chemical bond predissociation. Energy-dependent behavior of the rate constant perfectly correlates with that of the molecular structural change in the N-D bond length, providing unprecedented crucial information about how vibrational energy flows into the reaction coordinate on the adiabatic potential energy surfaces.
尽管其具有深远意义，但由振动耦合驱动的过渡态附近的分子结构变化在很大程度上仍未得到探索，使得化学反应的一个关键方面笼罩在不确定性之中。在此，通过对大幅度振动运动的光谱表征揭示了化学键断裂边缘反应通量的动力学行为。S-甲胺（CHND）的高激发内转子态报告了分子接近过渡态时的结构变化，表明准自由内旋转与反应坐标强烈耦合，因为它们的能量接近N-D化学键预解离反应势垒的最大值。速率常数的能量依赖行为与N-D键长的分子结构变化行为完美相关，为振动能量如何在绝热势能面上流入反应坐标提供了前所未有的关键信息。
