LAUSR

Collisions between cold polar molecules represent a fascinating research frontier but have proven hard to probe experimentally. We report measurements of inelastic cross sections for collisions between nitric oxide (NO) and deuterated ammonia (ND3) molecules at energies between 0.1 and 580 centimeter−1, with full quantum state resolution. At energies below the ~100-centimeter−1 well depth of the interaction potential, we observed backward glories originating from peculiar U-turn trajectories. At energies below 0.2 centimeter−1, we observed a breakdown of the Langevin capture model, which we interpreted in terms of a suppressed mutual polarization during the collision, effectively switching off the molecular dipole moments. Scattering calculations based on an ab initio NO-ND3 potential energy surface revealed the crucial role of near-degenerate rotational levels with opposite parity in low-energy dipolar collisions. Description From hot to near-ultracold collisions Despite decades of research, the ability to precisely study molecular collision dynamics is one of the main challenges in molecular physics, especially at low collision energies, which are generally accessible only to certain molecular species. Using Stark deceleration, hexapole state selection, merged beam scattering, and velocity map imaging techniques accompanied by quantum mechanical calculations, Tang et al. performed a detailed study of inelastic scattering between two polar molecules, NO and ND3, at collision energies spanning nearly four orders of magnitude between 0.1 and 580 centimeter−1. The authors achieved full quantum state resolution and observed transitions between quite different mechanisms across this range. The presented combination of techniques sets a new benchmark in the field and could be applied to a variety of dipole-dipole systems. —YS A state-of-the-art experiment over a large dynamic range covers completely different collision mechanisms for NO and ND3.