Formation of Complex Organic Molecules in Cold Interstellar Environments through non-diffusive grain-surface and ice-mantle chemistry

摘要: A prevailing theory for the interstellar production of complex organic molecules (COMs) involves formation on warm dust-grain surfaces, via diffusion and reaction radicals produced through grain-surface photodissociation stable molecules. However, some gas-phase O-bearing COMs, notably acetaldehyde(CH$_3$CHO), methyl formate(CH$_3$OCHO), dimethyl ether(CH$_3$OCH$_3$), are now observed at very low temperatures, challenging scenario. Here, we introduce a selection new non-diffusive mechanisms into an astrochemical model, to account failure standard diffusive picture provide more generalized scenario COM grains. New generic rate formulations provided cases where: (i) formed by reactions occurring close another reactant, producing immediate follow-on reaction; (ii) in excited state, allowing them overcome activation barriers react with nearby molecules; (iii) photo-dissociation partner, followed reaction. Each process occurs without large radicals. The significantly enhance cold abundances, successfully reproducing key observational results prestellar core L1544. H-abstraction from recombination, plays crucial role amplifying chemical desorption gas phase. UV-induced chemistry produces significant abundances bulk ices, which retained grains may persist later stages. O$_2$ is also strongly mantle though photolysis, suggesting cometary could indeed be interstellar.