  Nuclear isomers are populated in the rapid neutron capture process (r
process) of nucleosynthesis. The r process may cover a wide range of
temperatures, potentially starting from several tens of GK (several MeV) and
then cooling as material is ejected from the event. As the r-process
environment cools, isomers can freeze out of thermal equilibrium or be directly
populated as astrophysical isomers (astromers). Two key behaviors of astromers
-- ground state<->isomer transition rates and thermalization temperatures --
are determined by direct transition rates between pairs of nuclear states. We
perform a sensitivity study to constrain the effects of unknown transitions on
astromer behavior. We also introduce a categorization of astromers that
describes their potential effects in hot environments. We provide a table of
neutron-rich isomers that includes the astromer type, thermalization
temperature, and key unmeasured transition rates.
