Radiative feedback from ionized gas

H2 formation in metal-free gas occurs via the intermediate H − or H+2 ions. Destruction of these ions by photodissociation therefore serves to suppress H2 formation. In this paper, I highlight the fact that several processes that occur in ionized primordial gas produce photons energetic enough to photodissociate H− or H+2 and outline how to compute the photodissociation rates produced by a particular distribution of ionized gas. I also show that there are circumstances of interest, such as during the growth of H ii regions around the first stars, in which this previously overlooked form of radiative feedback is of considerable importance.