Schematic representation of the stereo-dynamical effect of the collision between the two reaction partners, Si⁺ and H₂S, in two limiting cases: a) for an approach at θ = 90° (i.e. perpendicular to the principal C₂ axis), the ion probes the interaction with the HOMO orbital of the H₂S molecule, favouring the formation of the MIN1 intermediate; b) as the ion approaches along the nodal plane (θ = 0°), no orbital overlap exists, thus leading to a non-reactive collision.