Quantum state-resolved molecular dipolar collisions over four decades of energy.

Tang, Guoqiang; Besemer, Matthieu; Kuijpers, Stach; Groenenboom, Gerrit C; van der Avoird, Ad; Karman, Tijs; van de Meerakker, Sebastiaan Y T · Science · 2023

basic_science · Level V

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Abstract

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 (ND<sub>3</sub>) molecules at energies between 0.1 and 580 centimeter<sup>-1</sup>, with full quantum state resolution. At energies below the ~100-centimeter<sup>-1</sup> well depth of the interaction potential, we observed backward glories originating from peculiar U-turn trajectories. At energies below 0.2 centimeter<sup>-1</sup>, 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-ND<sub>3</sub> potential energy surface revealed the crucial role of near-degenerate rotational levels with opposite parity in low-energy dipolar collisions.