  We study the H2 photodissociation regions around OB stars in primordial gas
clouds whose virial temperatures are between a few hundred and a few thousand
Kelvin. In such small objects, a single O star can photodissociate a mass equal
to that of the cloud itself. As a result, the clouds deplete their molecular
coolant and cannot cool in a free-fall time, and subsequent star formation is
totally quenched. This indicates that stars do not form efficiently in small
objects and that these objects contribute little to the reionization of the
universe.
