  H2 formation in metal-free gas occurs via the intermediate H- or H2+ 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 H2+ 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 HII regions
around the first stars, in which this previously overlooked form of radiative
feedback is of considerable importance.
