Notes. The MPM function is MPM(A, $\frac{A_{\text{des}}}{A_{\text{R}}}$, ΔE) = A/[1 + $\frac{A_{\text{des}}}{A_{\text{R}}}$], with A_des the pre-exponential factor of the adsorbed molecule (s⁻¹), A_R the pre-exponential factor of the adsorbed molecule ionisation (s⁻¹), and ΔE the difference in the activation energies from the Arrhenius equations controlling the adsorption of molecules onto the solid and the ionisation of the adsorbed molecule onto the solid surface (J.mol⁻¹). R is the ideal gas constant and T(z) the atmospheric temperature at altitude z (Berland et al. 1997; Taysum et al. 2024).

θ_Lang is the water ice surface coverage as defined by Kippenberger et al. (2019): ${\theta }_{\text{Lang}}=\frac{K_{\text{Lang}}[\text{HCl}]}{1+K_{\text{Lang}}[\text{HCl}]}$, with K_Lang = 9.6 × 10⁻¹¹ cm³.mol⁻¹ and [HCl] the number density of HCl (mol.cm⁻³).

[20] - Zhang et al. (2022), [21] - Seisel et al. (2005). For other references, see footnote of Table A.2