Collision‐induced spin‐orbit relaxation of highly vibrationally excited NO near 1 K

Abstract State‐to‐state scattering studies of vibrationally excited molecules in the cold regime extend inelastic scattering investigations into a new territory. Here, we present differential cross‐sections for superelastic scattering of spin‐orbit excited nitric oxide (NO) (v = 10, Ω = 1.5, j = 1.5) with argon near 1 K utilizing our recently developed near‐copropagating beam technique, and compare these to quantum scattering calculations on coupled cluster and multi‐reference potential energy surfaces. At these collision energies, the scattering is mainly governed by resonances and provides a platform to assess the accuracy of the attractive part of the difference potential for the NO–Ar system, which has remained untested. Quantum scattering calculations for such inelastic processes on high‐quality potential energy surfaces at thermal energies have largely been successful at reproducing the key features of experimental results, but cold spin‐orbit changing collisions are shown to test the limits of the current theoretical state‐of‐the‐art. The experimental results clearly exhibit backscattering centered around 3.5 cm−1 collision energy suggesting a scattering resonance; such resonances have never been detected for the well‐studied NO–Ar system. A partial wave analysis based on a multireference potential energy surface suggests the enhanced backscattering arises from overlapping resonances associated with the highest partial wave contributions. Key points We have achieved state‐to‐state spin‐orbit changing collisions of highly vibrationally excited NO with Ar near 1 K utilizing the near‐copropagating beam technique. The experiment reveals the influence of quantum scattering resonances for the well‐studied NO–Ar system for the first time. The results are found to challenge the current theoretical state‐of‐the‐art.