Irradiation of dust in molecular clouds. I. UV doses

Abstract

The fluxes of anomalous cosmic rays inside typical molecular clouds produced during collisions of stars with clouds are calculated. The charged particles formed in the cloud in the neighborhood of the star are accelerated in a shock front in the astrosphere by known statistical mechanisms to energies on the order of a few 100 MeV. It is shown that protons and α-particles with energies in the 1 keV ≤ E ≤ 10 GeV range penetrate deeply enough that, over the time of 1-5 hundred thousand years a star is passing through a cloud, they produce sufficient irradiation doses for the ice mantle of dust particles such that the cumulative effect owing to multiple passages would exceed a threshold value on the order of 0.1-1 eV/amu. The possible use of these results for astrophysical interpretation of laboratory experiments on the irradiation of H2O:CH3OH:NH3:CO ice mixtures is discussed. The complex organic substances formed by radiation-chemical transformation may play an important role in the prebiological evolution of the dust component of molecular clouds.