Differential cross sections for spin-orbit changing collisions of highly vibrationally excited NO near 1 K.

We have employed a “near-copropagating” beam configuration with a 4° intersection angle at the interaction region for scattering experiments which allows us to control the collision energy over a very a broad range, from around 1 K to far above room temperature. We have illustrated this for collisions of highly vibrationally excited NO molecules prepared in single quantum states using simulated emission pumping coupled with velocity map imaging detection. Here we present investigations of the collision-induced spin-orbit relaxation for collisions between vibrationally excited NO molecules (v=10) with Ar near 1 K utilizing the near-copropagating beams over a collision energy range from 1.5 cm^-1 to 3.5 cm^-1 . The excess energy available due to electronic deexcitation which is manifested in the NO recoil energy provides the platform to study collisions near cold limit while yielding a velocity map image from which the state-to-state DCSs can be extracted. The measured DCSs were compared with predicted DCSs from 2D and 3D quantum scattering calculations involving both multireference configuration interaction and couple cluster potential energy surfaces. The experimental results are found to present a challenge to current state-of-the-art electronic structure calculations.