Quantum mechanics aims to “micromanage” the details of collisions between atoms and molecules. However, it's hard to discern all the subtleties under high-energy conditions. Vogels et al. slowed down two intersecting beams of helium atoms and nitric oxide (NO) molecules to a relative crawl in order to characterize the collisions precisely. The data revealed short-lived resonances that matched theoretical predictions remarkably well—a striking feat on both sides, given the challenge of accurately modeling NO's unpaired electron. The study highlights chemists' increasingly sophisticated understanding of collision dynamics.
Science, this issue p. 787
Molecular scattering behavior has generally proven difficult to study at low collision energies. We formed a molecular beam of OH radicals with a narrow velocity distribution and a tunable absolute velocity by passing the beam through a Stark decelerator. The transition probabilities for inelastic scattering of the OH radicals with Xe atoms were measured as a function of the collision energy in the range of 50 to 400 wavenumbers, with an overall energy resolution of about 13 wavenumbers. The behavior of the cross-sections for inelastic scattering near the energetic thresholds was accurately measured, and excellent agreement was obtained with cross-sections derived from coupled-channel calculations on ab initio computed potential energy surfaces.
