Parity-Resolved State-to-State Cross Sections for Inelastic Scattering of NO X 2Π1/2 (v = 20, J = 0.5, e/f) from He: A Comparison between Crossed Molecular Beams Experiments and ab Initio Theory

Relative state-to-state cross sections for inelastic collisions between NO X 2 Π 1/2 ( v = 20, J = 0.5, e or f ) and He have been determined in a crossed molecular beam setup at a collision energy of 195 cm -1 . Efficient initial state preparation of the NO molecules is achieved by stimulated emission pumping by way of the NO B 2 Π 1/2 ( v = 5) state. The rotational state distribution of the inelastically scattered NO molecules is probed by laser induced fluorescence through the A 2 Σ + ( v = 3) state. The measured cross sections are compared with close-coupled quantum scattering calculations on both a recently reported ab initio potential energy surface (PES) and an extension of this PES which takes into account the elongation of the NO bond in v = 20. In the latter calculations, the highly vibrationally excited molecule is treated as a rigid rotor with a bond length equal to the average of the v = 20 level. Even with such an apparently drastic assumption, agreement between the experimental results and the scattering calculations on the latter PES is excellent.