Chemistry. Close encounters

No chemical reaction can take place without a collision between atoms or molecules. State-of-the-art experimental and theoretical techniques are providing ever more detailed insights into how such collisions proceed. In his Perspective, Crim highlights the report by Lorenz et al., who have succeeded in determining not only the amount but also the sense of rotation of NO molecules after collision with argon atoms. The results can only be explained when subtle quantum mechanical effects are considered.