Enhanced formation of interstellar complex organic molecules on carbon monoxide ice

Abstract

We investigated the role of carbon monoxide ice in the chemical evolution of prestellar cores using astrochemical rate equation models. We constrained the ratios of the binding energies on CO ice and H2O ice for a series of adsorbates deemed important in diffusive chemistry on H2O ices. We later included these ratios in our chemical reaction network model, where the binding and diffusion energies of icy species vary as a function of the surface composition. When the surface coverage of CO increases, the model shows an enhancement of O-bearing complex organic molecules especially those that formed from the intermediate products of CO hydrogenation (e.g., HCO) and CH3/CH2. Because the binding energy of CH3/CH2 is in the right range, its diffusion rate increases significantly with CO coverage. At T >14 K and with less influence, enhanced diffusion of HCO also contributes to the increase in the abundances of complex organic molecules. We find, however, that chemistry is not always enhanced on CO ice and that the temperature and cosmic ray ionization rate of each astronomical object is crucial for this particular chemistry, revealing a highly non trivial behavior that needs to be addressed on a per-case basis. Our results are highly relevant in the context of interstellar ice observations with JWST.