Small hydrocarbon particle erosion in a hot gas A comparative study

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 (10(4)-10(8) 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 (less than or similar to 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 approximate to 10(5)-10(7) 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.