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 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.

Differential Cross Sections for Cold, State-to-State Spin–Orbit Changing Collisions of NO(v = 10) with Neon

“…A schematic of the experimental setup and its key components are shown in Figure . More detailed information about the apparatus can be found elsewhere. − We note the latest version of the dual beam valve design includes one modification to improve its operation and reliability. Rather than using a ferrule and an O-ring compression to seal the reservoir we replaced it with two double X-profile o-rings on each plunger itself.…”

“…Zare and co-workers have also recently used intrabeam scattering to probe resonances for inelastic collisions of vibrationally excited H 2 , albeit without explicit control over the collision energy. ,, Another way of achieving low collision energies is to use a low intersection angle for the two molecular beams. This technique was successfully demonstrated by Bergeat et al using an apparatus with an adjustable intersection angle (down to 12.5°) coupled with time-of-flight detection. − We recently introduced a novel near-copropagating beam technique where we achieved an intersection angle of 4° to study collisions of vibrationally excited NO molecules with Ar. , We reported DCSs for spin–orbit conserving collisions as well as spin–orbit changing collisions of NO ( v = 10) with Ar at collision energies well above room temperature down to ∼2 K, along with the state-of-the-art quantum scattering calculations. , …”

When experiment challenges theory: Scattering of vibrationally excited molecules in the cold collision energy regime

“…This came in the form of the initial spin-orbit and/or rotational state energy. In the study highlighted herein, 37 angular distributions leading to the spin-orbit changing transition |v = 10, Ω = All in all, the highlighted combined experimental and theoretical study sets a new standard for our understanding of cold collisions.…”

“…The above rendered the single‐reference coupled‐cluster method used in previous treatments of NO($$^2\Pi _{\frac{1}{2}},v=0$$) inadequate. Therefore, the authors of the highlighted paper 37 constructed a new coupled‐cluster PES as well as a multireference configuration‐interaction (MRCI) PES and carried out full‐fledged (3D) QMCC calculations on both PESs. These tour‐de‐force calculations reproduced quite well the experimental differential cross sections and defined a new state of the art in scattering calculations.…”

“…Second, for such a highly excited vibrational state, both the long-and short-range interactions are affected, triggering nonadiabatic effects involving rotational and spin-orbit degrees of freedom. The above rendered the single-reference coupled-cluster method used in previous treat-ments of NO( 2 Π 1 2 , v = 0) inadequate.Therefore, the authors of the highlighted paper37 constructed a new coupled-cluster PES as well as a multireference configuration-interaction (MRCI) PES and carried out full-fledged (3D) QMCC calculations on both PESs. These tour-deforce calculations reproduced quite well the experimental differential cross sections and defined a new state of the art in scattering calculations.…”