标题： 通过非扩散性颗粒表面和冰层化学在寒冷星际环境中形成复杂有机分子 显示英文标题

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

摘要： 一种关于星际环境中复杂有机分子（COMs）产生的主流理论认为，这些分子是在温暖的尘埃颗粒表面通过自由基的扩散和反应形成的，这些自由基是通过稳定分子在颗粒表面的光解产生的。 然而，一些气相中的含氧COMs，特别是乙醛（CH$_3$CHO）、甲酸甲酯（CH$_3$OCHO）和二甲醚（CH$_3$OCH$_3$），现在在非常低温下被观测到，这挑战了温暖情景的假设。 在此，我们向天体化学模型中引入了一系列新的非扩散机制，以解释标准扩散图景的失败，并提供一个更通用的星际颗粒上COM形成场景。 对于以下情况提供了新的通用速率公式：（i）自由基通过靠近另一个反应物的反应形成，产生立即的后续反应；（ii）自由基以激发态形成，使其能够克服活化能垒与附近的稳定分子反应；（iii）自由基通过靠近反应伙伴的光解形成，随后立即发生反应。 每种过程都不涉及大自由基的扩散。 新机制显著增强了冷态COM的丰度，成功再现了预恒星核心L1544的关键观测结果。 从颗粒表面的COM中抽取H原子，随后发生重组，在增强化学脱附进入气相中起着关键作用。 紫外线诱导的化学在体冰中产生了显著的COM丰度，这些COM保留在颗粒上，并可能持续到后期阶段。 O$_2$也在包层中通过光解强烈形成，表明彗星中的O$_2$确实可能是星际的。 显示英文摘要

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