Lack of M-preserving propensities in rotationally inelastic collisions of NO(X 2Π1/2)

An expansion of the collision-frame scattering amplitude for JM→J′M′ transitions in irreducible tensor components facilitates the investigation of M-preserving propensities when quantization refers to the geometric or kinetic apse vectors. Specifically one can demonstrate that M preservation can be expected for processes where backward scattering dominates, but not for transitions which are forward peaked. For forward scattered processes involving open-shell diatomics, either even or odd changes in M (apse quantization) will be dominant, depending on the e/f symmetry label of the initial and final wave functions. These formal results will be illustrated by close-coupling calculations on collisions of NO(X 2Π1/2).