Chemical reaction dynamics are studied to monitor and understand the concerted motion of several atoms while they rearrange from reactants to products. When the number of atoms involved increases, the number of pathways, transition states and product channels also increases and rapidly presents a challenge to experiment and theory. Here we disentangle the dynamics of the competition between bimolecular nucleophilic substitution (S_N2) and base-induced elimination (E2) in the polyatomic reaction F⁻ + CH₃CH₂Cl. We find quantitative agreement for the energy- and angle-differential reactive scattering cross-sections between ion-imaging experiments and quasi-classical trajectory simulations on a 21-dimensional potential energy hypersurface. The anti-E2 pathway is most important, but the S_N2 pathway becomes more relevant as the collision energy is increased. In both cases the reaction is dominated by direct dynamics. Our study presents atomic-level dynamics of a major benchmark reaction in physical organic chemistry, thereby pushing the number of atoms for detailed reaction dynamics studies to a size that allows applications in many areas of complex chemical networks and environments.

研究化学反应动力学以监测和了解几个原子在从反应物重新排列到产物时的协同运动。当涉及的原子数量增加时，途径、过渡态和产物通道的数量也会增加，并迅速对实验和理论提出挑战。^{在这里，我们解开了多原子反应 F −}  + CH ₃ CH _{2中双分子亲核取代 (S N} 2) 和碱诱导消除 (E2)之间的竞争动力学Cl。我们发现离子成像实验和 21 维势能超表面上的准经典轨迹模拟之间的能量和角度微分反应散射截面的定量一致性。抗-E2 通路最重要，但随着碰撞能量的增加，S _N 2 通路变得更加相关。在这两种情况下，反应都受直接动力学支配。我们的研究展示了物理有机化学中主要基准反应的原子级动力学，从而将用于详细反应动力学研究的原子数量推至允许在复杂化学网络和环境的许多领域中应用的规模。