Ar ∗ ( 3P 2) / Kr ∗ ( 3P 0,2) + N 2(X) excitation transfer collisions: final state rotational alignment

The alignment of the rotational angular momentum J' of the N 2(C; v', J') final state is investigated in a wide range of collision energies 80 <E (meV) <2000 by analyzing the polarization of the fluorescence of the C → B transition. For the exothermic Ar ∗ + N 2 system the alignment is nearly energy-independent in the thermal range; the value A ≈ 0.4 indicates a preference for J' perpendicular to the initial relative velocity. At superthermal energies we observe a decrease to A ≈ 0 at E ≈ 2 eV, indicating an isotropic distribution of the direction of J'. The alignment is independent of the final vibrational state for v' = 0 and 1. For the endothermic Kr ∗ + N 2 system, where the different thresholds for the 3P 0 and 3P 2 states allow us to obtain the fine structure dependence of the alignment, we observe A ≈ 0.15 for 3P 0 and A ≈ 0.25 for 3P 2. For energies far above threshold we observe a decrease to A = 0.05 at E = 5 eV, which is attributed to the behaviour of the 3P 2 state.