Astron. Astrophys. 337, 847-858 (1998)

Dust formation in stellar winds

VII. Kinetic nucleation theory for chemical non-equilibrium in the gas phase

A.B.C. Patzer ¹, A. Gauger ² and E. Sedlmayr <sup>1

1</sup> Technische Universität Berlin, Institut für Astronomie und Astrophysik, PN 8-1, Hardenbergstr. 36, D-10623 Berlin, Germany
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Received 3 March 1998 / Accepted 19 March 1998

Abstract

We present a new theoretical formulation of the nucleation process of solid particles from the gas phase with special emphasis on the effects of chemical non-equilibrium in the gas phase and thermal non-equilibrium between the gas and the clusters or dust grains. In the derivation of the nucleation rates from kinetic theory and from thermodynamic arguments thermal and chemical non-equilibrium are straightforwardly included. A hierarchy of expressions for the stationary nucleation rate is given, ranging from a system of equations, which determines the rate, to an approximate analytic expression in the case of a single dominating growth species, which requires only the time scales of the growth processes and the Gibb's free energy change for the formation of clusters.

Key words: molecular processes dust, extinction circumstellar matter stars: late-type

Send offprint requests to: A.B.C. Patzer

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Contents

• 1. Introduction
• 2. The master equation in the case of chemical and thermal non-equilibrium
  • 2.1. Master equation
  • 2.2. The growth and evaporation time scales
  • 2.3. Definition of the reference equilibrium state
  • 2.4. Application of the detailed balance
• 3. The stationary nucleation rate for chemical and thermal non-equilibrium
  • 3.1. A general expression for the stationary nucleation rate
  • 3.2. Analytic approximation of the nucleation rate for the case of a single dominating growth species
  • 3.3. Some remarks on the Gibbs free energy change and the equilibrium cluster size distribution
• 4. Summary
• Acknowledgements
• Appendix A: on the supersaturation ratio of N-clusters
• Appendix B: definition of the generalized departure coefficients
• References

© European Southern Observatory (ESO) 1998

Online publication: August 27, 1998
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