A prerequisite to gain a complete understanding of the most basic aspects of chemical reactions is the ability to perform experiments with complete control over the reactant degrees of freedom. By controlling these, details of a reaction mechanism can be investigated and ultimately manipulated. Here, we present a study of chemi-ionization—a fundamental energy-transfer reaction—under completely controlled conditions. The collision energy of the reagents was tuned from 0.02 K to 1,000 K, with the orientation of the excited Ne atom relative to Ar fully specified by an external magnetic field. Chemi-ionization of Ne(³P₂) and Ar in these conditions enables a detailed investigation of how the reaction proceeds, and provides us with a means to control the branching ratio between the two possible reaction outcomes. The merged-beam experimental technique used here allows access to a low-energy regime in which the atoms dynamically reorient into a favourable configuration for reaction, irrespective of their initial orientations.

全面了解化学反应的最基本方面的先决条件是能够完全控制反应物的自由度进行实验。通过控制这些，可以研究并最终操纵反应机理的细节。在这里，我们介绍了在完全受控的条件下化学电离（一种基本的能量转移反应）的研究。试剂的碰撞能量从0.02 K调整到1,000 K，被激发的Ne原子相对于Ar的取向完全由外部磁场指定。Ne（³ P ₂）和Ar在这些条件下可以详细研究反应的进行方式，并为我们提供了一种方法来控制两种可能的反应结果之间的支化比。此处使用的合并束实验技术允许进入低能状态，在这种状态下，原子无论其初始方向如何都动态地重新定向为有利的构型以进行反应。