H₂Cl⁺ OPR as a function of the gas temperature: (i) at thermal equilibirum (solid pink line); (ii) obtained with a full model considering a hydrogen abstraction and a proton hop mechanism for respectively the H₂ + HCl⁺ and formation reactions (dashed red curve); (iii) obtained with a model considering full scrambling for all the reactions involving nuclear-spin forms (dashed blue curves); (iv) taken from a simple analytical formula and designated OPR₀, this model represents scrambling via reaction (4) at steady state with the OPR for H₂ treated as thermal (Neufeld et al. 2015) (solid cyan). The time evolution of the complete scrambling model is depicted on the second panel where the H₂Cl⁺ OPR is represented in green for a time of 1.5 × 10³ yr as an indicative reference.