Radial abundances (with respect to n(H₂)) of protons, and its deuterated isotopologs and electrons (indicated in the figure). Panel a) is a reproduction of the middle panel of Fig. 6 in Sipilä et al. (2010) (showing abundances at t = 10⁶ years), calculated with the version of the chemical code used in that paper (see text). The two middle panels use the same physical model as in panel a), but chemical evolution has been calculated with the present version of the chemical code (see text) with quantum tunneling turned either on (panel b)) or off (panel c)). Panel d) plots again the same physical situation but calculated with the new reaction network presented in this paper, with initial heavy element abundances set to zero.