a) Schematic representation of the Si⁺−H₂S reactive system. The H₂S molecule is bound within the xz plane, while the Si⁺ ion moves within the yz plane, at a fixed distance from the molecule (i.e. the equilibrium Si-S bond length R = 3.8 Å) and with an angle, θ, with respect to the xz plane. As the ion moves, it probes the electrostatic potential from z = −R to z = +R. b) Energy barrier (E_T) as a function of θ: the electrostatic potential increases as the ion moves from θ = 0° to 180° in the yz plane, with an increase of the repulsive contribution given by the hydrogen atoms. The barrier is obtained as a difference between the effective potential calculated at θ = θ′ and θ = 0°. The inset is an expansion of the yellow area in the main graph.