Photodissociation and photoionisation of atoms and molecules of
  astrophysical interest
  A new collection of photodissociation and photoionisation cross sections for
102 atoms and molecules of astrochemical interest has been assembled, along
with a brief review of the basic processes involved. These have been used to
calculate dissociation and ionisation rates, with uncertainties, in a standard
ultraviolet interstellar radiation field (ISRF) and wavelength-dependent
radiation fields. The new ISRF rates generally agree within 30% with our
previous compilations, with a few notable exceptions. The reduction of rates in
shielded regions was calculated as a function of dust, molecular and atomic
hydrogen, atomic C, and self-shielding column densities. The relative
importance of shielding types depends on the species in question and the dust
optical properties. The new data are publicly available from the Leiden
photodissociation and ionisation database.
  Sensitivity of rates to variation of temperature and isotope, and cross
section uncertainties, are tested. Tests were conducted with an
interstellar-cloud chemical model, and find general agreement (within a factor
of two) with the previous iteration of the Leiden database for the ISRF, and
order-of-magnitude variations assuming various kinds of stellar radiation. The
newly parameterised dust-shielding factors makes a factor-of-two difference to
many atomic and molecular abundances relative to parameters currently in the
UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray
induced photodissociation and ionisation rates differ from current standard
values up to a factor of 5. Under high temperature and cosmic-ray-flux
conditions the new rates alter the equilibrium abundances of abundant dark
cloud abundances by up to a factor of two. The partial cross sections for H2O
and NH3 photodissociation forming OH, O, NH2 and NH are also evaluated and lead
to radiation-field-dependent branching ratios.
