Cosmic rays are able to heat interstellar dust grains. This may enhance
molecule mobility in icy mantles that have accumulated on the grains in dark
cloud cores. A three-phase astrochemical model was used to investigate the
molecule mobility in interstellar ices. Specifically, diffusion through pores
in ice between the subsurface mantle and outer surface, assisted by whole-grain
heating, was considered. It was found that the pores can serve as an efficient
transport route for light species. The diffusion of chemical radicals from the
mantle to the outer surface are most effective. These species accumulate in the
mantle because of photodissociation by the cosmic-ray induced photons. The
faster diffusion of hydrogen within the warm ice enhances the hydrogenation of
radicals on pore surfaces. The overall result of the whole grain
heating-induced radial diffusion in ice are higher abundances of the ice
species whose synthesis involve light radicals. Examples of stable species
synthesized this way include the complex organic molecules, OCS, H2O2 and
cyanoplyynes
