Evolution of the gas temperature as a function of the number density of hydrogen nuclei, with (solid lines) and without (dashed lines) accounting for the effect of photodetachment of H⁻ ions by Lyα photons. The colors denote calculations assuming different background radiation fields which are assumed only to dissociate H₂ molecules. With no photodetachment the temperatures remain too low for DCBH formation in all cases, but with this effect included DCBH formation can occur for a background radiation field with J₂₁~ 10³. As in Fig. 1, here ℬ = 1, corresponding to uniform Lyman α emission within the collapsing cloud.