Polarization effects in the ionization cross section for collisions of excited Ne**{(2p)5(3p); J = 3}) with Ar : a sensitive probe for "locking" phenomena

At a collision energy E=0.1 eV we see a large polarization effect Qion*Mj*=0,1/QionMj*=3=2.5, decreasing to 1.4 for E=1 eV. A two-state basis is used for the autoionization width of the p and s orientations of the (2p)-1 core hole, resulting in a preference for the O=0,1 molecular states as seen at 0.1 eV. The energy dependence is due to the decrease of ‘‘locking’’ of J to the internuclear axis with increasing angular velocity f¿, leading to the semiclassical criterion ¿prec=4f¿ for the transition from a space-fixed to a body-fixed description of J.