Physical structure and quantities of the Orion Bar model as a function of visual extinction. (a) Gas temperature and H₂ density. (b) Fractional abundances of each H₂ vibrational level. (c) Contribution of each individual H₂ vibrational level to the N + H₂(v) reaction rate coefficient and denoted as k_v(T) × f(v), with f(v) = n(H₂, v)/n(H₂). (d) Total formation rate coefficient (black curves) and N and NH abundance profiles.