Photodissociation of interstellar ArH⁺

¹ LERMA and UMR 8112, Observatoire de Paris, place J. Janssen, 92190 Meudon, France
e-mail: evelyne.roueff@obspm.fr
² Fachbereich C, Physikalische und Theoretische Chemie, Bergische Universität Wuppertal, Gaußstrasse 20, 42097 Wuppertal, Germany
e-mail: alexeev@uni-wuppertal.de
³ LERMA and UMR 8112, Observatoire de Paris, place J. Janssen, 92190 Meudon, France
e-mail: jacques.lebourlot@obspm.fr

Received: 17 February 2014
Accepted: 5 April 2014

Abstract

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.