Differential cross sections for fine structure transitions in O( ³P₂)+Ar Collisions

We present experimental and theoretical differential cross sections for the fine structure changing process Ar + O(³P₂)→Ar + O(³P_jmj) with (j,m_j)=(1,1), (1,0), and (0,0). The measured cross sections refer to a collision energy of 3.2 kcal/mol, and were obtained from Doppler line shapes associated with (2+1) resonance-enhanced multiphoton ionization of O(³P_jmj) after scattering in a crossed-beam apparatus. The theoretical results are based on ³Σ^- and ³Π potential curves obtained from high quality ab initia calculations, and on quantum coupled-channel calculations. The calculated differential cross sections show strong Stuckelberg oscillations, with similar magnitudes and phases for all three final states. With slight adjustment (0.03 Å) of the hard wall on the 3Σ^- curve, the calculated angular distributions match up well with the corresponding experimental results, much better than is found using previously derived empirical potentials. At the same time, the integral total cross sections obtained from the ab initia measurements are in satisfactory agreement with previous measurements.