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+ were computed in an ab initio approach that includes an 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 for a very small unshielded cloud surrounded on all sides by the standard unshielded InterStellar Radiation Field (ISRF) model is equal to 9.9 × 10-12 s-1 and 1.9 × 10-9 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 mainly depends on the molecular fraction.