  Aims. Chemical databases such as the UMIST Database for Astrochemistry (UDFA)
are indispensable in the numerical modeling of astrochemical networks. Several
of the listed reactions in the UDFA have properties that are problematic in
numerical computations: Some are parametrized in a way that leads to extremely
divergent behavior for low kinetic temperatures. Other reactions possess
multiple entries that are each valid in a different temperature regime, but
have no smooth transition when switching from one to another. Numerically, this
introduces many difficulties.We present corrected parametrizations for these
sets of reactions in the UDFA06 database.
  Methods. From the tabulated parametrization in UDFA, we created artificial
data points and used a Levenberg-Marquardt algorithm to find a set of improved
fit parameters without divergent behavior for low temperatures. For reactions
with multiple entries in the database that each possess a different temperature
regime, we present one joint parametrization that is designed to be valid over
the whole cumulative temperature range of all individual reactions.
  Results. We show that it is possible to parametrize numerically problematic
reactions from UDFA in a form that avoids low temperature divergence.
Additionally, we demonstrate that it is possible to give a collective
parametrization for reaction rate coefficients of reactions with multiple
entries in UDFA. We present these new fitted values in tabulated form.
