Alignment and orientation of Ar+ in He+-Ar collisions

We have measured the alignment and orientation parameters of the² F ₇ ^2/0 and² F ₅ ^2/0 states of Ar⁺ formed in the two-electron process; He⁺+Ar→He(1s ²)+Ar⁺(3p ⁴4p′). These have been measured at a collision energy of 0.25 keV/amu and for scattering angles ranging from 0.94° to 3.75°. First, by comparing the orientation parameter for the Ar⁺[(3p ⁴[¹ D]4p′² F ₇ ^2/0 ] and the Ar⁺[(3p ⁴[¹ D]4p′² F ₅ ^2/0 ] states, we have experimentally determined the importance of the spin-dependent interactions for the present collision system, by testing the Percival-Seaton hypothesis of spin independence. If the Percival-Seaton hypothesis holds for this system, the orientation parameter should beJ-independent. Secondly, the magnitude of the orientation parameter can be interpreted as resulting from the collective circulation of the unexcited 3p ⁴ electrons and the excited 4p electron. The direction of this collective circulation is compared to the propensity rule for colliding di-atom systems.