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State-to-state differential cross sections for rotationally inelastic collisions of vibrationally excited NO with Ar have been measured in a near-copropagating crossed beam experiment at collision energies of 530 and 30 cm–1. Stimulated emission pumping (SEP) to prepare NO in specific rovibrational levels is coupled with direct-current slice velocity map imaging to obtain a direct measurement of the differential cross sections. The use of nearly copropagating beams to achieve low NO–Ar collision energies and broad collision energy tuning capability are also demonstrated. The experimental differential cross sections (DCSs) for NO in v = 10 in specific rotational and parity states are compared with the corresponding DCSs predicted for NO in v = 0 obtained from quantum mechanical close coupling calculations to highlight the differences between the NO­(v = 10)–Ar and NO­(v = 0)–Ar interaction potentials.

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 nearcopropagating 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.

We have developed an apparatus capable of performing intrabeam and near-copropagating beam scattering experiments at collision energies from room temperature to below 1 K where interesting quantum phenomena can be observed. A detailed description of the major components of the apparatus, single and dual molecular beam valves, high speed chopper, and the discharge source, is presented. With the intrabeam scattering setup, a novel dual-slit chopper permits collision energies down to millikelvins with a collision energy spread of 20%. With the near-copropagating beam configuration, state-to-state differential cross sections for rotationally inelastic collisions of highly vibrationally excited NO molecules with Ar have been measured at broadly tunable energies documenting the versatility of the instrument. Future applications in stereodynamics and cold state-to-state collisions of vibrationally excited polyatomic molecules are briefly discussed.

Inelastic scattering processes have proven a powerful means of investigating molecular interactions, and much current effort is focused on the cold and ultracold regime where quantum phenomena are clearly manifested. Studies of collisions of the open shell nitric oxide (NO) molecule have been central in this effort since the pioneering work of Houston and co-workers in the early 1990s. State-to-state scattering of vibrationally excited molecules in the cold regime introduces challenges that test the suitability of current theoretical methods for ab initio determination of intermolecular potentials, and concomitant electronically nonadiabatic processes raise the bar further. Here we report measurements of differential cross sections for state-to-state spin–orbit changing collisions of NO (v = 10, Ω″ = 1.5, and j″ = 1.5) with neon from 2.3 to 3.5 cm–1 collision energy using our recently developed near-copropagating beam technique. The experimental results are compared with those obtained from quantum scattering calculations on a high-level set of coupled cluster potential energy surfaces and are shown to be in good agreement. The theoretical results suggest that distinct backscattering in the 2.3 cm–1 case arises from overlapping resonances.