One in about seventy collisions of He with singlet CH₂ produces triplet CH₂, even though the spin-orbit coupling of singlet and triplet CH₂ is weak and virtually unaffected by He. Mixed-state gateways are invoked as the key intermediates in such molecules, where the level structure is sparse and the spin-orbit couplings are weak. Experimental eigenstate-resolved kinetic spectroscopy, double-resonance saturation recovery and saturation transfer experiments provide a new, direct, and detailed look at the role of mixed states in the collision-induced intersystem crossing process. Spin-preserving, rotationally inelastic collisions, along with coherent evolution of non-stationary spin in mixed state pairs, interrupted by frequent dephasing collisions provides a conceptual framework for an efficient spin changing process that never invokes the direct interaction of the collision partner with the spin of the target molecule.