Astron. Astrophys. 323, 534-540 (1997)

The ionisation state of PAHs in interstellar environments

E. Dartois and L. d'Hendecourt

IAS-CNRS, Université Paris XI, Batiment 121, F-91405 Orsay Cedex, France

Received 23 July 1996 / Accepted 23 December 1996

Abstract

We present an ionisation model for Polycyclic Aromatic Hydrocarbon (PAH) molecules from which we determine the various size dependant ionisation states expected in different space environments. Maps of ionisation regimes are derived. They allow the estimate of the ionisation fraction of PAH for any given set of parameters (electron density, flux factor and temperature) assuming a typical PAH size of 50 carbon atoms. Moreover, a particular astronomical case is considered: the variation in ionisation states with depth in a typical dense cloud illuminated by a bright B1.5V star.

Key words: molecular data molecular processes ISM: molecules ISM: general

Send offprint requests to: E. Dartois

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Contents

• 1. Introduction
• 2. The model
  • 2.1. Photoionisation of PAHs
  • 2.2. Recombination of PAHs
  • 2.3. Ionisation equilibrium
• 3. Ionisation in various environments
• 4. Ionisation regimes
• 5. An example: ionisation in a dense cloud
• 6. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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