Simulating the formation of massive seed black holes in the early
  Universe. II: Impact of rate coefficient uncertainties
  We investigate how uncertainties in the chemical and cooling rate
coefficients relevant for a metal-free gas influence our ability to determine
the critical ultraviolet field strength required to suppress H2 cooling in
high-redshift atomic cooling halos. The suppression of H2 cooling is a
necessary prerequisite for the gas to undergo direct collapse and form an
intermediate mass black hole. These black holes can then act as seeds for the
growth of the supermassive black holes (SMBHs) observed at redshifts $z \sim
6$. The viability of this model for SMBH formation depends on the critical
ultraviolet field strength, Jcrit: if this is too large, then too few seeds
will form to explain the observed number density of SMBHs. We show in this
paper that there are five key chemical reactions whose rate coefficients are
uncertain enough to significantly affect Jcrit. The most important of these is
the collisional ionization of hydrogen by collisions with other hydrogen atoms,
as the rate for this process is very poorly constrained at the low energies
relevant for direct collapse. The total uncertainty introduced into Jcrit by
this and the other four reactions could in the worst case approach a factor of
five. We also show that the use of outdated or inappropriate values for the
rates of some chemical reactions in previous studies of the direct collapse
mechanism may have significantly affected the values of Jcrit determined by
these studies.
