Parity-resolved state-to-state cross sections for inelastic scattering of NO X (2)Pi(1/2) (upsilon = 20, J = 0.5, elf) 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) Pi(1/2) (upsilon = 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) Pi(1/2) (upsilon = 5) state. The rotational state distribution of the inelastically scattered NO molecules is probed by laser induced fluorescence through the A (2) Sigma(+) (upsilon = 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 upsilon = 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 upsilon = 20 level. Even with such an apparently drastic assumption, agreement between the experimental results and the scattering calculations on the latter PES is excellent.