Thermal (LTE) rate coefficients for reaction R₂ implemented in our simulations (see text for details). Also, relative abundances f_v for H₂(v≤2) are shown as the dotted lines. The experiment-based rate coefficients are consistent with the measurements at temperatures between 400 and 700 K (Johnsen et al. 1980). For reference, the low-temperature measurements (Schauer et al. 1989) recommended for astrochemical applications (McElroy et al. 2013) are ∼3×10⁻¹⁴ cm³s⁻¹.