Small hydrocarbon particle erosion in a hot gas

A comparative study

¹ Institut d’Astrophysique Spatiale (IAS), UMR 8617, CNRS/Université Paris-Sud, 91405 Orsay, France
e-mail: marco.bocchio@ias.u-psud.fr
² Department of Physics and Astronomy, Western University, London, Ontario N6A 3K7, Canada
³ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, Paris Sciences et Lettres, 5 place Jules Janssen, 92195 Meudon, France

Received: 29 May 2012
Accepted: 12 July 2012

Abstract

Aims. We compare the classical and molecular approaches for small particle erosion, in an overlapping particle size domain, to model dust destruction in a hot gas.

Methods. We calculated and compared the carbon ejection rate constant for a-C:H grains and PAHs (with 50 to 5000 carbon atoms) in a hot gas (10⁴−10⁸ K).

Results. The classical approach does not take into account electron collisions nor electronic interactions, which are shown, using the molecular approach, to be important for small grains ( ≲ 1000 carbon atoms). For N_C ≤ 1000 the two approaches diverge but for larger grains they are in very good agreement for a wide range of temperatures (T ≈ 10⁵−10⁷ K).

Conclusions. To quantify the erosion of small hydrocarbon grains in a hot gas a molecular approach, rather than classical sputtering, needs to be adopted. This then indicates that small hydrocarbon nano-particles (with N_C < 1000 or a < 3 nm) cannot be abundant in a hot coronal-type gas, be it galactic hot ionised medium or nearby intergalactic medium, because they are rapidly destroyed by dissociation resulting from electronic excitations induced by electron collisions.