  Clouds containing molecular dark matter in quantities relevant for star
formation may exist in minihaloes of the type of cold dark matter included in
many cosmological simulations or in the regions of some galaxies extending far
beyond their currently known boundaries. We have systematically explored
parameter space to identify conditions under which plane-parallel clouds
contain sufficient column densities of molecular dark matter that they could be
reservoirs for future star formation. Such clouds would be undetected or at
least appear by current observational criteria to be uninteresting from the
perspective of star formation. We use a time-dependent PDR code to produce
theoretical models of the chemistry and emission arising in clouds for our
chosen region of parameter space. We then select a subset of model clouds with
levels of emission that are low enough to be undetectable or at least
overlooked by current surveys. The existence of significant column densities of
cold molecular dark matter requires that the background radiation field be
several or more orders of magnitude weaker than that in the solar
neighbourhood. Lower turbulent velocities and cosmic ray induced ionization
rates than typically associated with molecular material within a kpc of the Sun
are also required for the molecular matter to be dark. We find that there is a
large region within the parameter space that results in clouds that might
contain a significant mass of molecular gas whilst remaining effectively
undetectable or at least not particularly noticeable in surveys. We note
briefly conditions under which molecular dark matter may contain a dynamically
interesting mass.
