Reaction scheme for the formation of CH₃OH and its deuterated isotopologues. The upper half shows the applied ‘forward reactions’ (addition reactions), either adding H (in the horizontal direction) or D (in the vertical direction). The lower half shows the employed ‘backward reactions’ (abstraction reactions), reacting with H or D and thereby removing a H₂, HD, or D₂ molecule. The values on top of the arrows indicate, if existing, the activation energies, E_A, in 10³ K. There are always two values for the abstraction reactions. The first one gives the value for the reaction with H, the second for the reaction with D. Note that our reaction scheme also includes two ‘substitution reactions’, exchanging one D atom for a H atom in H₂CO and HDCO, which are not shown here for the sake of clarity.