Ar∗ (3P2) / Kr∗ (3P0,2) + N2(X) excitation transfer collisions: Final state rotational alignment Original Research Article

The alignment of the rotational angular momentum J′ of the N2(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∗ + N2 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∗ + N2 system, where the different thresholds for the 3P0 and 3P2 states allow us to obtain the fine structure dependence of the alignment, we observe A ≈ 0.15 for 3P0 and A ≈ 0.25 for 3P2. 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 3P2 state.