Statistical models provide a powerful and useful class of approximations for calculating reaction rates by bypassing the need for detailed, and often difficult, dynamical considerations. Such approaches invariably invoke specific assumptions about the extent of intramolecular vibrational energy flow in the system. However, the nature of the transition to the statistical regime as a function of the molecular parameters is far from being completely understood. Here, we use tools from nonlinear dynamics to study the transition to statisticality in a model unimolecular reaction by explicitly visualizing the high dimensional classical phase space. We identify generic features in the phase space involving the intersection of two or more independent anharmonic resonances and show that the presence of correlated, but chaotic, intramolecular dynamics near such junctions leads to nonstatisticality. Interestingly, akin to the stability of asteroids in the Solar System, molecules can stay protected from dissociation at the junctions for several picoseconds due to the phenomenon of stable chaos.

统计模型通过绕过详细且通常困难的动态考虑的需要，为计算反应速率提供了一类强大而有用的近似值。这些方法总是引用关于系统中分子内振动能流程度的特定假设。然而，作为分子参数函数的统计机制转变的性质远未被完全理解。在这里，我们使用非线性动力学工具通过显式可视化高维经典相空间来研究模型单分子反应中向统计性的转变。我们在涉及两个或多个独立非谐共振的交集的相空间中识别一般特征，并表明相关但混乱的存在，这种连接点附近的分子内动力学导致非统计性。有趣的是，类似于太阳系中小行星的稳定性，由于稳定​​的混沌现象，分子可以在连接处保持几皮秒的解离保护。