Photodissociation of interstellar ArH+
  Aims. Following the recent detection of 36ArH+ in the Crab nebula spectrum,
we have computed the photodissociation rate of ArH+ in order to constrain the
physical processes at work in this environment. Methods. Photodissociation
cross sections of ArH+ are computed in an ab initio approach including explicit
account of spin-orbit coupling. Results. We report the photodissociation cross
section of ArH+ as a function of wavelength. Photodissociation probabilities
are derived for different impinging radiation fields.The photodissociation
probability of for a very small unshielded cloud surrounded on all sides by the
unshielded InterStellar Radiation Field (ISRF) model described by Draine (1978)
is equal to 9.9e-12 s-1 and 1.9e-9 s-1 in the Crab nebula conditions. The
dependence on the visual extinction is obtained by using the Meudon Photon
Dominated Region (PDR) code and corresponding analytical fits are provided.
Conclusions. These data will help to produce a realistic chemical network to
interpret the observations. Photodissociation of ArH+ is found to be moderate
and the presence of this molecular ion is mainly dependent on the molecular
fraction
