State-to-State Differential Cross Sections for Inelastic Collisions of NO Radicals with para-H 2 and ortho-D 2 .

We present state-to-state differential cross sections for collisions of NO molecules (X2 Π1/2 , j = 1/2f) with para-H2 and ortho-D2 molecules, at a collision energy of 510 and 450 cm-1 , respectively. The angular scattering distributions for various final states of the NO radical are measured with high resolution using a crossed molecular beam apparatus that employs the combination of Stark deceleration and velocity map imaging. Rotational rainbows as well as diffraction oscillations are fully resolved in the scattering images. The observed angular scattering distributions are in excellent agreement with the cross sections obtained from quantum close-coupling scattering calculations based on recently computed NO-H2 potential energy surfaces, except for excitation of NO into the j = 7/2f channel. For this particular inelastic channel, a significant discrepancy with theory is observed, despite various additional measurements and calculations, at present, not understood.