Restructuring and destruction of hydrocarbon dust in the interstellar medium

A model of key processes influencing the evolution of a hydrocarbon grain of an arbitrary size under astrophysical conditions corresponding to ionized hydrogen regions (HII regions) and supernova remnants is presented. The considered processes include aromatization and photodestruction, sputtering by electrons and ions, and shattering due to collisions between grains. The model can be used to simulate the grain size distribution and the aromatization degree during the evolution of HII regions and supernova remnants for a specified radiation field, relative velocity of gas and dust, etc. The contribution of various processes to the evolution of hydrocarbon dust grains for parameters typical for the interstellar medium of our Galaxy is presented. Small grains (less than 50 carbon atoms) should be fully aromatized in the general interstellar medium. If larger grains initially have an aliphatic structure, it is preserved to a substantial extent. Variations in the size distribution of the grains due to their mutual collisions depend appreciably on the adopted initial size distribution. For the MRN initial distribution a significant redistribution of grain sizes is obtained, which increases the mass fraction of smaller grains. Characteristic for an initial distribution from the work of Jones et al. (2013), with high initial fraction of small grains, is a general decrease in the number of grains of all sizes.