Chemiluminescence and rotational alignment in Mn*(a 4DJ, a6DJ) + SO2 → MnO*(A′ 6Π, A6Σ+) + SO

Abstract

Measurements with ‘hot’ and ‘cold’ Mn atom beams, and analysis ia the multiple line-of-centres procedure, have enabled the determination of separate state-to-state translational excitation functions for Mn*(a⁴D_J, a⁶D_J) + SO₂ → MnO*(A′⁶Π, A⁶Σ⁺) + SO. All indicate either a narrow cone of acceptance for reaction or a fairly flat angular dependence of the barrier, a result also inferred from ab initio density functional theory calculations on the lowest quartet surface. With increasing collision energy, the barrier appears to shift forward, suggesting a transition from ‘ soft-sphere’ to ‘ hard-sphere’ dynamics. For Mn*(a⁴D_J) → MnO*(A⁶Σ⁺) the rotational alignment − 〈P₂(ĵ′·)〉 at first falls with increasing collision energy, indicating preferred coplanar reaction geometry, but this preference is absent in all other channels. Simple molecular orbital–electron transfer arguments rationalise these observations and suggest strongly that Mn*(a⁶D_J) reaction leads to SO*(a¹Δ) also.