2025ApJ...990..163B

We present the results of astrochemical modeling of complex organic molecules (COMs) in the ice and gas of the prestellar core L1544 with the recently updated MONACO rate equation-based model. The model includes, in particular, nondiffusive processes, new laboratory verified chemical routes for acetaldehyde and methane ice formation, and variations of H and H₂ desorption energies depending on the surface coverage by H₂ molecules. For the first time, we simultaneously reproduce the abundances of several oxygen-bearing COMs in the gas-phase, the approximate location of the peak of methanol emission, as well as the abundance of methanol in the icy mantles of L1544. Radical-radical reactions on the grain surface between species such as CH₃, CH₃O, and HCO efficiently proceed nondiffusively. COMs are delivered to the gas-phase via chemical desorption amplified by the loops of H-addition/abstraction surface reactions. However, gas-phase chemical reactions as well provide a noticeable input to the formation of COMs in the gas, but not to the COMs solid-state abundances. This particularly applies for CH₃CHO and CH₃OCH₃. The simulated abundances of COMs in the ice are in the range 1%-2% (for methyl formate ice) or ∼0.1% (for CH₃CHO and CH₃OCH₃) with respect to the abundance of H₂O ice. We stress a similarity between the simulated abundances of icy COMs in L1544 and the abundances of COMs in the gas-phase of hot cores/corinos. We compare our nondiffusive model with the diffusive model and provide constraints for the species' diffusion-to-desorption energy ratios.